Method and apparatus for force-based touch input

ABSTRACT

A force sensor for sensing a touch force applied to a touch surface is disclosed. The force sensor includes: a first element including an elastic element and a first capacitor plate having a first capacitive surface, the elastic element including at least part of the first capacitor plate; and a second element including a second capacitor plate opposed to the first capacitor plate; wherein transmission of at least part of the touch force through the elastic element contributes to a change in capacitance between the first capacitor plate and the second capacitor plate. The elastic element and the first capacitor plate may be integral. Other force sensors and methods for manufacturing said force sensors are also disclosed. Touch location devices suitable for use with the disclosed force sensors are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to concurrently filed and commonlyowned patent application entitled “Tangential Force Control in a TouchLocation Device,” hereby incorporated by reference in its entirety.

BACKGROUND

[0002] 1. Field of the Invention

[0003] The present invention relates to touch sensors and, moreparticularly, to force sensing touch location devices.

[0004] 2. Related Art

[0005] The ability to sense and measure the force and/or location of atouch applied to a surface is useful in a variety of contexts. As aresult, various systems have been developed in which force sensors areused to measure properties of a force (referred to herein as a “touchforce”) applied to a surface (referred to herein as a “touch surface”).Force sensors typically generate signals in response to the touch forcethat may be used, for example, to locate the position on the touchsurface at which the touch force is applied. A number of particularimplementations of this approach have been proposed, such as thatdescribed by Peronneau et al. in U.S. Pat. No. 3,657,475.

[0006] Such touch location is of particular interest when the touchsurface is that of a computer display, or that of a transparent overlayin front of a computer display. Furthermore the need for small,lightweight, and inexpensive devices that are capable of performingtouch location is increasing due to the proliferation of mobile andhandheld devices, such as personal digital assistants (PDAs). The touchscreens which perform this function may be built with a number ofpossible technologies. In addition to the force principle justmentioned, capacitive, resistive, acoustic, and infrared techniques areamong those that have been used.

[0007] The force principle has some strong potential advantages overthese competing techniques. Since force techniques may be applied to anyoverlay material, or indeed to the entire display itself, there is noneed to interpose materials or coatings with low durability or pooroptical properties. Also, since force is the basis of perceived touch,there is no problem with sensitivity seeming unpredictable to the user.With capacitive measurement, for instance, touch threshold varies withthe condition of the user's skin, and with interposed materials, such asa glove. Stylus contact typically gives no response. With resistivemeasurement, threshold force depends upon the size of the contact area,and so is very different between stylus and finger. Acoustic measurementdepends upon the absorptive characteristics of the touching material;and with infrared, a touch may register when there has been no contact.

[0008] In spite of these advantages of force-based technologies,resistive and capacitive technologies have dominated in the touch screenmarket. This reflects residual difficulties with known force techniques,which must be overcome to realize the potential of force technology.

[0009] Among these difficulties are:

[0010] Excessive force sensor size—especially width and thickness.

[0011] Excessive sensitivity to transverse forces, leading toinaccuracy.

[0012] Excessive force sensor cost and complexity.

[0013] Excessive sensitivity to deformations of the touch surface or itssupporting structure, leading to inaccuracy.

[0014] The need to keep the touch surface mechanically independent ofthe application bezel that encloses the touch surface, which makes itdifficult to integrate the touch screen into the larger structure, andmakes it difficult to provide a good liquid and dust seal.

[0015] In modern touch applications, it is extremely important thatprovisions for touch force location and/or measurement not increase thesize nor dictate the appearance of the touch-equipped device. This isespecially true in portable and handheld applications. Conventionalforce sensors of the type required are typically much thicker thanresistive or capacitive films, thereby potentially increasing thethickness of devices that incorporate such force sensors compared todevices that incorporate resistive or capacitive sensors. Sinceconventional force sensors of the type required cannot easily be madetransparent, they cannot be placed in front of an active display area.As a result, devices including such conventional force sensors musttypically be made wider than a resistive- or capacitive-based device toaccommodate the force sensors. Thus force-based touch is potentiallydisadvantageous with respect both to overall device thickness and width,when compared to other kinds of conventional touch sensors.

[0016] Thus it is seen that the prior art fails to teach how forcesensors may be made sufficiently narrow, thin, and inexpensive.

[0017] A touch force applied to a touch surface has both a componentthat is normal to the touch plane (the “perpendicular component”) and acomponent that is parallel to the touch plane (the “tangentialcomponent”). The presence of a tangential component can introduce errorsin the computed touch location. Various techniques for reducing theerrors introduced by tangential forces are described in more detail inthe co-pending application entitled “Tangential Force Control in a TouchLocation Device.”

[0018] In many applications it may be desirable for an application bezelto press firmly around the edges of a touch-equipped display or displayoverlay module. This arrangement provides a dust and/or liquid seal, andmay also serve to stiffen and align the bezel. With force-sensingtouch-location devices, however, the bezel does not typically restdirectly against a force sensitive structure, since the variablehandling forces thereby transmitted would interfere excessively withtouch location accuracy. The prior art does not teach satisfactorymethods for sealing, nor for sufficiently diverting bezel forces inforce-based based touch systems.

SUMMARY

[0019] In one of its aspects, the invention provides a novel capacitiveforce sensor. The sensor comprises a principal element, and anessentially planar support. The principal element combines the functionsof elastic energy storage and one capacitor plate, and may be as simpleas a plane rectangle of thin spring metal. As described in more detailbelow, the sensor may be implemented with a small number of mechanicalparts and a very small capacitive gap, making the sensor easy andinexpensive to manufacture and making the sensor particularly applicablefor use in mobile and handheld devices. It should be stressed, however,that sensors made in accordance with the invention may be of greatadvantage in a wide range of devices, sizes, and applications. To date,they have been successfully used in devices with a working diagonal offrom 4″to 15″, and supported touch surface assemblies weighing from 0.6ounces to nearly 4 pounds.

[0020] For example, in one aspect of the invention, a force sensor forsensing a touch force applied to a touch surface is provided. The forcesensor comprises: a first element including an elastic element and afirst capacitor plate having a first capacitive surface, the elasticelement including at least part of the first capacitor plate; and asecond element including a second capacitor plate opposed to the firstcapacitor plate; wherein transmission of at least part of the touchforce through the elastic element contributes to a change in capacitancebetween the first capacitor plate and the second capacitor plate.Various other force sensors are also provided, as described in moredetail below.

[0021] In yet another aspect of the invention, a force sensing touchlocation device is provided. The force sensing touch location devicecomprises: a touch surface; a bezel enclosing a first portion of thetouch surface; and force transmission means including an enclosingportion enclosing a second portion of the touch surface, said forcetransmission means having a stiffness greater than that of the bezel,wherein the force transmission means includes a path to transmit forcefrom the bezel to a region not including the touch surface.

[0022] In a further aspect of the invention, a force sensing touchlocation device is provided. The force sensing touch location devicecomprises: a touch surface defining a touch plane; a first rigid member;a contoured first film coupled to the touch surface and the first rigidmember to form a first seal therebetween, the contoured first film beingcompliant along an axis normal to the touch plane.

[0023] In another aspect of the invention, a method is provided formeasuring a touch force applied to a touch surface using one of theforce sensors described herein. The method comprises a step ofdeveloping a signal based on the change in capacitance between the firstcapacitor plate and the second capacitor plate of the force sensor. Theamplitude of the signal may be a monotonic function of the change incapacitance between the first capacitor plate and the second capacitorplate. The method may include a step of measuring a property of thetouch force, such as the amplitude of a component of the touch forcethat is perpendicular to the touch surface, based on the signal. 85. Themethod may include a step of measuring a location on the touch surfaceat which the touch force is applied.

[0024] In yet another aspect of the invention, a method is provided forseparating a first capacitor plate from a second capacitor plate in aforce sensor by a desired volume. The method comprises steps of:disposing a separator between a support surface and a principal elementincluding the first capacitor plate to maintain a separation of at leastthe desired volume between the first capacitor plate and the secondcapacitor plate; coupling at least one region of the principal elementto at least one region of the support surface; and removing theseparator, whereby the first capacitor plate and the second capacitorplate remain separated by at least the desired volume in an unloadedstate of the force sensor. The support surface may, for example, be thesecond capacitor plate.

[0025] In a further aspect of the invention, a method is provided forseparating a first capacitor plate from a second capacitor plate in aforce sensor by a desired volume. The method comprises steps of:disposing a predetermined substrate containing particles of controlledsize between a support surface and a principal element including thefirst capacitor plate to produce a separation of at least the desiredvolume between the first capacitor plate and the second capacitor plate;and coupling at least one region of the principal element to at leastone region of the support surface to maintain the separation of at leastthe desired volume between the first capacitor plate and the secondcapacitor plate.

[0026] In another aspect of the invention, a method for manufacturing aforce sensor is provided. The method comprises steps of: selecting aprinciple element including a substantially flat surface and a firstcapacitive surface; disposing the first capacitive surface in oppositionto a second capacitive surface; and forming an elevated elastic featureinto the substantially flat surface, whereby transmission of a forcethrough the elevated elastic feature contributes to a change incapacitance between the first capacitor plate and the second capacitorplate.

[0027] In another aspect of the invention, a force sensing touchlocation device is provided. The force sensing touch location devicecomprises: a touch surface structure to which a touch force may beapplied, the touch force including a perpendicular component that isperpendicular to a touch surface of the touch surface structure and atangential component that is tangential to the touch surface of thetouch surface structure; a supporting structure; at least one forcesensor, in communication with the touch surface and the supportingstructure, to measure properties of the touch force; lateral restraintmeans, in contact with both the touch surface structure and thesupporting structure, for impeding lateral motion of the touch surfacestructure without substantially impeding transmission of theperpendicular component of the touch force through the at least oneforce sensor.

[0028] Other features and advantages of various embodiments of thepresent invention will become apparent from the following descriptionand from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1A is an exploded drawing of a touch screen module of a firstpreferred embodiment, as might be used against the face of a separateLCD module.

[0030]FIG. 1B is a partial cross-section of the module of FIG. 1A,intersecting the center of a sensor.

[0031]FIG. 2 is a cross sectional view of a first embodiment, in atypical application installation.

[0032]FIG. 3 is a cross sectional view of a second embodiment, in atypical application installation.

[0033]FIG. 4 is a partially schematic cross-sectional view of a generaltouch-locating system, illustrating reduction of tangential force errorsaccording to one embodiment of the invention.

[0034]FIGS. 5A through 5C provide partial cross sectional viewsillustrating the use of a flat suspension film or beam used as a lateralstiffening means.

[0035]FIG. 6 is a partial cross sectional view of a lateral stiffeningand/or lateral restraint means with extended range of vertical motion,and directionally selective lateral stiffening.

[0036]FIGS. 7A through 7C are partial cross sectional views of furthervariations on the lateral stiffening means.

[0037]FIG. 8 is a partial cross sectional view of a touch system with afield-replaceable touch surface protector and liquid/dust seal.

[0038]FIG. 9A is a cross sectional view of a larger sensor of a typebuilt in accordance with the invention.

[0039]FIG. 9B is an exploded perspective view of the sensor assembly ofFIG. 9A.

[0040]FIG. 10A is a cross sectional view of a smaller sensor of a typebuilt in accordance with the invention.

[0041]FIG. 10B is an exploded perspective view of the sensor assembly ofFIG. 10A.

[0042]FIG. 11 is a vertically exaggerated cross section of a sensorvariation employing a nonuniform gap, built in accordance with oneembodiment of the present invention.

[0043]FIGS. 12A through 12D are plan views depicting possible variationsin the outline and mounting arrangement of principal elements of sensorsaccording to embodiments of the invention.

[0044]FIGS. 13A and 13B are vertically exaggerated cross sectionsdepicting possible variations in the thickness distribution of principalelements of sensors according to embodiments of the invention.

[0045]FIG. 14A is a plan view of a sensor variation employing aprincipal element with simply supported ends, according to embodimentsof the invention.

[0046]FIG. 14B is a side view of the plastic spacer used in the sensorvariation of FIG. 14A.

[0047]FIG. 14C is a partial cross-sectional view of a touch locationdevice employing variations of aspects of the invention, including thesensor variation of FIG. 14A.

[0048]FIGS. 15A and 15B are exploded and cross-sectional views,respectively, of a sensor variation incorporating nonmetallic elasticportions, according to embodiments of the invention.

[0049]FIG. 15C is a cross-sectional view of a related sensor variationincorporating nonmetallic elastic portions, according to one embodimentof the invention.

DETAILED DESCRIPTION

[0050] In one of its aspects, the invention provides a novel capacitiveforce sensor. As described in more detail below, the sensor may beimplemented with a small number of mechanical parts and a very smallcapacitive gap, making the sensor easy and inexpensive to manufactureand making the sensor widely applicable, but particularly so for use inmobile and handheld devices. The sensor comprises a principal element,and an essentially planar support. The principal element combines thefunctions of elastic energy storage and one capacitor plate, and may beas simple as a plane rectangle of thin spring metal. The principalelement is held in close parallel alignment with the essentially planarsupport by mechanical contacts at one or more bearing points or areas.These may be under the two ends of the rectangular principal element,though many other arrangements, such as cantilever, cross, disk, etc.,will readily occur to one of ordinary skill in the art, and are withinthe scope of the invention. The support also bears a thin conductiveregion opposed to a portion of the principal element away from thecontacts, which functions as a second capacitor plate, or counterelectrode. The mechanical contacts may provide either simple, or clampedsupport to the principal element, viewed as a load bearing beam. Thecontacts however, should be designed to minimize dissipative orfrictional effects. The principal element receives forces through anupper loading contact, at a point or area opposite the counterelectrode. Components of force perpendicular to the support surfacedeflect the principal element so as to change the distance separating itfrom the counter electrode, thus altering the capacitance therebetween.If the mechanical contacts provide clamped end constraint, it isdesirable that this be stiff; that is, most of the distance changeoccasioned by a force should be due to flexure of the principal element,rather than twisting of the mechanical contact areas. Although cleanlyelastic clamped end constraints may be tolerable, where they engenderonly a systematic change in sensitivity, better reproducibility andfreedom from hysteresis usually may be obtained if the end constraintsare stiff clamped end constraints, or fully flexible simple supports,such as pivots.

[0051] The essentially planar support surface may be part of aninterconnect system, such as a printed wiring board or flexible circuitwith appropriate stiffeners. The counter electrode may comprise a land,or foil, within the context of such an interconnect. The mechanicalcontacts may also constitute electrical contacts, and may beaccomplished by soldering the ends of the principal element to otherlands in the support plane.

[0052] Force may be measured as the ratio of an exciting AC voltage tothe current it forces through the sensor. As a matter of practice, aconstant current may be applied by a feedback circuit, and the excitingvoltage measured (as in Roberts, U.S. Pat. No. 5,376,948); or a constantexciting voltage may be applied, and the reciprocal of the resultingcurrent computed. The latter method may enable use of a somewhat simplerinterconnect, and provides a somewhat more convenient opportunity forsubtracting off estimates of fixed strays which might otherwise degradelinearity of response. The force-responsive signals derived from theforce sensors may be processed to yield touch location information inaccordance with principles known in the art.

[0053] The curvature resulting from flexure of the principal element isnot ideal, but by confining the counter electrode to an area near thecenter of the principal element, potential nonlinearities of responsemay be reduced to a level acceptable for use in a touch locatingapplication. Other provisions for improved linearity may also be made,as described below.

[0054] A force sensor has a direction of sensitivity, such that atranslational force of given magnitude creates greatest output whenapplied in that direction, and no output when applied at right angles tothat direction. A displacement sensor has an analogous direction ofsensitivity with respect to applied pure translational displacements. Aforce sensor is said herein to have an axis of sensitivity that passesthrough its elastic center in its direction of sensitivity. Adisplacement sensor may be taken to have an axis of sensitivity lying inits direction of sensitivity, and so located that relative rotation ofthe two sides about points in the axis tend to produce no output.

[0055] It is desirable that a force sensor have a precisely determinedaxis of sensitivity, and that this axis be easily and precisely aligned,as desired, with respect to the enclosing application. The thin, planarnature of the sensor provided in various embodiments of the inventionsatisfies this need naturally. It is also desirable for the force sensorto be unresponsive to any moment couples passing through it. For a forcesensor comprising a displacement sensor sensing the displacement acrossan elastic means, this requires that the displacement sensor's axis ofsensitivity pass through the elastic center of the elastic means.Sensors provided in various embodiments of the invention accomplish thisgoal by making the principal element and its contacts symmetrical undera 180 degree rotation about the axis of sensitivity.

[0056] Potential moment sensitivity may be further reduced by providinga rotational softener at the loading contact. A bump, or other elevatedcentral feature in the principal element, may serve as a pivot providingthis function. Locating this feature in the principal element itself hasthe further advantage of providing the force sensor with a determinedsensitivity. When force is transmitted from an overlying surfacecontacting the bump, changes in relative alignment leave the region ofload transmission unchanged with respect to the force sensor.

[0057] Forces and moments may be transmitted through a sensor that arenot those the sensor is intended to measure. If the sensor is notperfectly constructed and aligned, it may have some sensitivity tothese, leading to errors of measurement. In addition, unmonitored forcesand moments may be part of a pattern including monitored forces, suchthat the equations for locating touch may not be evaluated accuratelywithout measurements of the full pattern being available.

[0058] Various aspects of the invention provide for the reduction orelimination of these unmonitored forces or moments.

[0059] In a first aspect, embodiments of the invention may employ arotational softening means to reduce or eliminate moments transmittedthrough a force sensor. In one embodiment, such a rotational softenermay comprise a soft elastic body, such as a small elastomeric slab, or astiffer element, such as a portion of a metal stamping, bent orprolonged in the direction of sensitivity. In another embodiment, it maycomprise a pivot, operating without receptacle against a hard surface,or with self-forming receptacle, against a softer surface.

[0060] One benefit of rotational softening may obtain where the touchsurface structure is not fully rigid, such that some small local flexureoccurs near a point of touch. Such local flexure may lead to substantialtouch location error, even with perfectly constructed and alignedsensors, if the sensor on its support from below is not substantiallysofter in rotation than the attachment offered from above by the touchsurface structure. In effect, a sensor connection with excessiverotational stiffness can support a nearby touching finger in part byusing the intervening portion of the touch surface structure as acantilever, thereby obtaining more of the perpendicular force than wouldbe ideally presumed. A distortion of the position of reported touchlocations results, which distortion is sensitive to details of thestiffness relationships. Rotational softening may be employed to preventthe appearance of such a pattern combining unmonitored sensor momentwith balancing spurious perpendicular force components.

[0061] Rotational softening may thus be of particular benefit when usedwith a touch surface structure that is thin and flat, and thuscomparatively flexible, such as a flat overlay plate of minimalthickness.

[0062] Another benefit of rotational softening may obtain where thesensors are not perfectly constructed. Such sensors may give spuriousresponses to transmitted moments. A rotational softener may offergreatest reduction of the moment actually experienced by a force sensor,if it is located as close as possible thereto. This reduces theproduction of sensor moment in response to any lateral forcestransmitted. Thus rotational softening achieving the benefits of theinvention may be applied away from the plane of touch, and may beapplied close to the force sensors.

[0063] In a second aspect, embodiments of the invention may employ alateral softening means to reduce or eliminate forces transmittedthrough a force sensor at right angles to its nominal axis ofsensitivity. In one embodiment, such a rotational softener may comprisean elastic body, such as a small elastomeric slab. In anotherembodiment, it may comprise a pin, column, or ball, offering a pair ofpivots, softly elastic ends, or rolling surfaces offset from each otherby at least a small distance.

[0064] One benefit of rotational softening may obtain where tangentialforces applied to the touch surface are prevented from developing apattern of forces, such pattern combining spurious perpendicular sensorforces with lateral sensor force and moment to maintain overallequilibrium, as described in more detail below.

[0065] Another benefit of lateral softening may obtain where the sensorsare not perfectly constructed. Such sensors may give spurious responsesto forces at right angles to their nominal axis of sensitivity. Lateralsoftening may also reduce extra sensor moment potentially generated bysuch lateral forces, where the associated elastic center is not in thesensor center.

[0066] Combinations of lateral softening, rotational softening, andlateral stiffening may serve to establish necessary axes of sensitivitymore accurately than can be achieved through the construction of thesensors themselves. This follows in part from the large area over whichthe alignment of the plane of effect of the lateral stiffening means maybe established.

[0067] Many alternative embodiments of lateral and rotational softeningmeans will be evident to those of ordinary skill in the art, and arewithin the scope of the invention.

[0068] The method of forming a force sensor from a principal elementupon an essentially planar supporting surface provides strikingadvantages in simplicity and miniaturization.

[0069] In one embodiment of the present invention, where an essentiallyplanar support surface is comprised of a printed wiring board or otherplanar interconnect system, a force sensor is provided that includes aslittle as one, single, separately manufactured and handled part—theprincipal element described above. For example, the principal elementmay be as simple as a rectangle of plated spring steel, flat but for asmall bump pressed into the center. Mounting may be accomplished byreflowing solder under the ends of the principal element, while thecentral region is spaced from the counter electrode area with atemporary stainless-steel shim.

[0070] Alternatively, the solder employed may be mixed with a smallquantity of non-fusing particles of controlled size, and the presence ofthese may serve to establish the gap width during soldering. Surfacetension of the solder may suffice to draw the opposing surfaces againstthe particles. Yet again, the principal element may be provided withareas of slight offset pressed or otherwise formed into the ends, andthese may rest directly against the support. Such slightly offset areasmay take many forms, one being a slight displacement of the entire endtoward the support surface. Another entails forming one or more of thesmallest practicable bumps at each end, protruding by the degreenecessary to establish the desired gap. These offer some space undereach end for good solder reflow, and also minimize the likelihood oftrapped solder contaminants enlarging the gap.

[0071] Alternatives to the use of solder will be evident, including theuse of cements, such as conductive epoxy, and methods involvingindependent or indirect electrical connection to the mounted element.

[0072] By allowing construction from starting materials that areinherently flat, smooth, and true, which are then simply spaced apart asmall distance, various embodiments of the invention provide anextremely reliable and inexpensive method of achieving a very smallcapacitive gap. This small gap provides a high capacitance per unitarea, which allows the sensor area to be very small. The small gaprequires limited mechanical energy storage in the principal element,allowing the use of thin material. The small gap implies high sensorstiffness, which in turn implies high resonant frequencies, and isbeneficial for accurate measurement. The small area of the sensor meansthat flatness in the materials need be maintained over only a very shortdistance, thus making practical even smaller gaps in a virtuous circleof miniaturization.

[0073] Sensor designs provided by various embodiments of the presentinvention are subject to a simple scaling rule over fairly wide range ofsizes. A new design may be produced, which is N times shorter, N timesnarrower, and N squared times smaller in gap. If the originalproportions and material thickness are otherwise retained, the resultingsensor will retain the same capacitance, force range, and sensitivity asthe original. Since the area is N squared times smaller and the gap Nsquared times smaller, the capacitance is the same. Since the springrate is N squared times greater and the gap N squared times smaller, therelative capacitance change with force, i.e. the sensitivity, is thesame. Since the stressed portion of the principal element is N squaredtimes smaller in volume, but stores N squared times less energy for thesame applied force, it is exposed to the same stress levels. Since thedeviation of a warped surface from flat, scales as the square of thedistance over which the deviation is taken, the flatness requirement forthe materials used is unchanged. Note that “flatness” here refers todeviations of low spatial frequency; high frequency failures ofsmoothness may ultimately limit miniaturization scaled this way. It maybe noted, however, that ordinary spring steel and circuit boardmaterials are smooth enough to support gaps down to {fraction (1/1000)}of an inch, and probably substantially smaller.

[0074] In another of its aspects, the invention provides a novel meansfor performing accurate touch location measurements in the presence oftangential forces, even when the sensors are located well behind theplane of touch. This is accomplished with lateral stiffening means,which direct tangential touch forces away from the force sensors (e.g.,to the surrounding support structure). At the same time, perpendiculartouch force components pass predominantly through a mechanicallyseparate path to the force sensors. The lateral stiffening means istypically designed to have a plane of zero reaction moment to tangentialforces, which is co-incident with, or close to, the touch surface. Incases where lateral stiffness through other force paths is notinsignificant, the lateral stiffening means may be designed to achievethe same net effect for all paths collectively.

[0075] To simplify the design, and maximize reproducibility, force pathsother than the lateral stiffening means may be provided with explicitlateral softening means, such that essentially all tangential forcespass through the lateral stiffening means. The perpendicular force paththrough the sensors may be stiff, while the perpendicular force paththrough the lateral stiffening means may be soft. The latter isparticularly desirable in circumstances where interfering perpendiculardisplacements may occur across the lateral stiffening means, as mightresult from flexing in an overlay plate or its surrounding frame.Together, both provisions accomplish full segregation of the tangentialand perpendicular touch forces into separate paths.

[0076] The lateral stiffening means may, for example, be embodied in athin member or film, which joins a display or touch overlay to asurrounding frame. This film may bridge a small gap between the frameand the edge of the touch surface, where it attaches, or there may be alesser gap, and the film may carry above the touch surface a short waysbefore attaching to the touch surface. By being much thinner than it isbroad, yet composed of material of fairly high modulus, this film may bestiff to tangential movement of the touch surface, yet soft toperpendicular motion. The film may be made to bulge, or curve, somewhatabove and/or below the touch plane, thus increasing its vertical rangeof compliance. Such curvature also has the effect of restricting thelateral stiffening to the sides parallel to a tangential force, where itis transmitted through the film as shear, rather than compression orextension.

[0077] A lateral stiffening means, embodied as a completecircumferential edge film in or close to the plane of touch, may at thesame time constitute a liquid and/or dust seal.

[0078] Although in the embodiment described above the lateral stiffeningmeans is a thin member or film, this does not constitute a limitation ofthe present invention. Rather, the lateral stiffening means may take avariety of forms and be constructed from a variety of materials. Thelateral stiffening means need not be continuous, and is not limited toany particular modulus, aspect or shape. Rather, the lateral stiffeningmeans may include any structure that performs the function of lateralstiffening as described herein.

[0079] In another aspect of the invention, a thin or slender member orset of members may comprise a lateral restraint means, allowing assemblyof a force-sensing touch-location device to be maintained, withoutstrong attachments that fix the support surface structure by pathspassing through the force sensors. In such a device, the exactperpendicular operating position of the touch surface structure isestablished by perpendicularly stiff paths, such as through the forcesensors, that provide connection to the support structure independent ofthe lateral restraint means. In one embodiment, the touch surfacestructure may rest upon force sensors below, without attachment, andwithout any special receptacle or other provision on the touch surfacestructure for receiving contact with the force sensors, or needingcareful alignment thereto. The force sensors, whether mounted from thetouch surface structure above, or from the support structure below, maythus be provided with rotational softeners and/or lateral softenersoffering little or no strength but in compression. Many forms ofcurvature or elevated feature from either side at the perpendicularforce contacts may serve as a rotational softener, so long as localtouch surface flexure does not translate the point of contact by morethan the tolerable error in touch location. Perpendicular contact may bemaintained by preload means, which may be separate from the lateralrestraint means.

[0080] A lateral restraint means may be distinguished from a lateralstiffening means in that tangential touch forces may not necessarilypass through a lateral restraint means. The small, incremental forces ofa touch may instead follow stiffer paths through the force sensors orother connections, as dictated by friction. Larger lateral disturbances,however, overcome friction and cause minute sliding motions in thesepaths. These disturbances may comprise jolts in shipping and handling,for instance, or for large devices with a heavy touch surface structure,changes in orientation with respect to gravity. A lateral restraintmeans may absorb the brunt of such disturbances tangentially, protectingthe touch device structure, function, and accuracy from significantalteration. By reaching the upper limit of its perpendicular motion, alateral restraint means may also absorb a disturbance tending to liftthe sensors free of contact, although such function may be performed byseparate outward limit stops. A lateral restraint means may deflect farenough to be assisted by lateral limit stops during large, temporaryforces, but when these cease, it may restore satisfactory centering,free of continuing interference from stops.

[0081] A thin member or set of thin members may provide a lateralrestraint means that is simple and compact. It may add little or nothingto the thickness of a touch-location module or touch-enabled displaymodule. Such a thin member or set of members may further offer afavorably high ratio of lateral to perpendicular stiffness. Absent sucha high ratio, members sufficiently robust to provide good lateralrestraint may offer excessive vertical stiffness. In avoiding suchexcessive vertical stiffness, various embodiments of this aspect of theinvention avoid inaccuracy occasioned by parasitic force paths, such asmight pass through a seal. They also avoid the need for an excessivelythick and stiff touch surface structure or support structure inmitigation. Such thin members may flex softly in response toperpendicular displacement of the touch surface, but stiffly resisttangential displacement. Thus, a wire-like member, inclined at mostshallowly to the plane of touch, may serve to resist tangential forcesprimarily through end-on compression and extension, while being softlyflexible in transverse beam bending. So too, a sheet-like member maytransmit tangential force stiffly in shear, and possibly also incompression and extension, while responding to perpendiculardisplacement of the touch surface with soft beam bending transverse toits breadth. Where tangential force transmission is confined to shear,and where a lateral restraint means is not also a lateral stiffeningmeans, sheet-like members may provide an effective lateral restraintmeans, even though they incline steeply to the plane of touch. A lateralrestraint means may perform its function, even if not located in theplane of touch.

[0082] In another aspect of the invention, a thin frame means is wrappedclosely around the periphery of the overlay or supported display. Amajor benefit of this construction is the provision of a module whichhandles, mounts, and integrates with its surrounding application in amanner which is familiar from other touch technologies, is accepted, andis convenient. The frame means serves to divert perpendicular forcesfrom the application bezel normally present, so that there is no dangerof interference with the touch surface. The frame lip provides aconvenient rigid bearing edge to receive both a vertically compliantseal passing outward from the touch surface, and a smooth surface orother seal provision of the underside of the application bezel. Sinceperpendicular forces are of principal concern, a very thin verticalframe leg, embodies an application bezel support member, and serves tocarry bezel forces back to a stiff surface behind a touch module, suchas the surface of an LCD. With greater section depth, such a very thinleg also serves to carry back bezel forces when the frame surrounds asupported LCD.

[0083] FIGS. 1A-1B present a touch sensitive transparent overlay module101 including capacitive force sensors according to a first embodimentof the invention. The module 101 may be used to sense touches appliedby, for example, a finger, stylus, or other object. As described in moredetail below, in various embodiments of the present invention, themodule 101 may be used to sense properties of a touch force applied to atouch surface, such as the location at which the touch force is appliedto the touch surface and/or the magnitude of a component of the touchforce that is perpendicular to the touch surface.

[0084] The transparent overlay module 101 is proportioned as might beappropriate for use on an LCD display with a diagonal of 4 inches,though proportions and variations for other displays of other sizes willbe apparent to those of ordinary skill in the art. Transparent panel102, carrying touch surface 103 a, rests within frame 104 a. Capturedbetween panel 102 and frame 104 a are interconnect flex print 105, forcesensor principal elements 106, and lateral softening means 107. Preloadsprings 109 are fastened to the edges of panel 102 with cement 110. Theends of springs 109 engage holes 112 in frame 104 a when assembled,thereby applying a total compression of approximately two pounds to thestructures captured between panel 102 and frame 104 a. The flexedpositions of springs 109, as assembled, place them in straight linesalong the short edges of panel 102. Member 108 is a combination lateralstiffening means, lateral restraint means, and liquid/dust seal 108.Member 108 may also be referred to elsewhere herein simply as a lateralstiffening means, lateral restraint means, or seal, for ease ofexplication. Member 108 adheres to panel 102 and to the outer surfacesof the vertical flanges of frame 104 a, thereby securely centering panel102 within frame 104 a. When so centered, there is a small space betweenthe long sides of panel 102 and frame 104 a, and there is a small spacearound the nonattached portions of springs 109. Thus forces applied totouch surface 103 a can produce small perpendicular motions of panel 102without occasioning interference or scraping around its edges.

[0085] One embodiment of the capacitive force sensor of the presentinvention is now described in more detail. As will become apparent fromthe following description, FIG. 1A illustrates four capacitive forcesensors in assembly and FIG. 1B illustrates one of these capacitiveforce sensors in cross-section. In assembly, interconnect 105 isthreaded through apertures 111 in frame 104 a and dressed along andabove opposing horizontal flanges of frame 104 a as shown. Interconnect105 is fastened securely to frame 104 a under receiving regions ofprincipal elements 106, such that these regions achieve the effectivestiffness of frame 104 a. Such attachment may be achieved by providinginterconnect 105 with backside lands which are soldered to frame 104 a,or by cementing interconnect 105 to frame 104 a with epoxy resin, or byother known means. Elements 106 are secured to interconnect 105 bysoldering their ends to lands 113. By either the shape of principalelements 106, or by the assembly process which attaches them tointerconnect 105, there remains a small gap of determined width betweenprincipal elements 106 and counter-electrode lands 114. For the type ofassembly shown, this gap may be 0.0010 inch. A central dimple, or forcebearing 121, is pressed upward into each of principal elements 106.

[0086] Each of the force sensor principal elements 106 combines thefunctions of spring and capacitor plate. As perpendicular force isapplied to one of the bearings 121, flexure of the corresponding one ofthe principal elements 106 increases the capacitance between the centralportion of the principal element's underside and the corresponding oneof the counter-electrodes 114 (which are on the underside ofinterconnect 105). This change in capacitance may be measured to measurethe force applied to the surface 103 a. As shown in FIGS. 1A and 1B,each bearing 121, corresponding principal element 106, the correspondingreceiving region of interconnect 105, and the stiffening supportprovided thereto by frame 104 a, thus together constitute a forcesensor.

[0087] Although four force sensors are shown in FIG. 1A, it should beappreciated that any number of force sensors may be employed with aparticular device as may be appropriate for a particular application.Furthermore, although the force sensors are positioned close to thecorners of the overlay panel 102, this is not a limitation of thepresent invention.

[0088] Although a particular embodiment of the principal element 106 isshown in FIGS. 1A and 1B, more generally principal element 106 is anelectrically conductive elastic element that both stores elastic energyand acts as a capacitor plate in a force sensor. As a result of theprincipal element's elastic properties, the principal element 106 isdeflectable by a touch force applied to the touch surface 103 a. Thisdeflection causes a change in the capacitance between the principalelement and lands 113 (which act as capacitor plates that oppose theprincipal element 106). The principal element 106 thereby combines thefunctions of elastic energy storage and a capacitor plate in a small,thin, easily manufactured part.

[0089] Interconnect 105 provides electrical access to counter-electrodes114 and to principal elements 106 via lands 113, as necessary to provideseparate readings from the four force sensors so constituted. In oneembodiment of the present invention, each of the principal elements 106is the only component of each force sensor that must be manufactured andhandled individually.

[0090] In embodiments of the present invention such as that depicted inFIGS. 1A-1B, lateral softening means 107 may comprise small puncheddisks of stainless-steel tape, backed by a typically soft acrylicadhesive. The adhesive surfaces are applied to the backside of panel102, such that the metal surfaces press against bearings 121 afterassembly. The effect of the small area of soft acrylic adhesive, soconfined, is to substantially reduce the lateral forces generatedbetween principal elements 106 and panel 102, generated in reaction totiny lateral displacements of the under surface of panel 102.

[0091] As described above, in one embodiment each of the principalelements 106 is provided with a bearing 121. The bearing 121 may providea region of load transmission from the touch surface 103 a to thecorresponding principal element 106. Although the bearings 121 are shownas small bumps located at the centers of the principal elements 106, itshould be appreciated that other elevated features may be provided inthe principal elements 106 to perform the same function.

[0092] The bearings 121 may serve as pivots. Locating the bearings 121in the principal elements 106 themselves has the advantage of providingthe force sensor with a determined sensitivity. When force istransmitted from an overlying surface (such as the touch surface 103 a)contacting one of the bearings 121, changes in relative alignment of thecorresponding one of the principal elements 106 and the overlyingsurface (e.g., the undersurface of panel 102) leave the region of loadtransmission substantially unchanged. This effect becomes morepronounced as the size of the bearings 121 and the corresponding regionof contact decreases. Note that, as shown in the embodiment shown inFIG. 1B, the bearings 121 need not be disposed within receptacles.

[0093] Further details appropriate for the embodiment depicted in FIGS.1A-1B may now be considered. Frame 104 a may be of mild steel, plated orcoated for corrosion resistance. It may be made from 0.020 in. sheet,stamped, folded, or drawn by any of a variety of known techniques. Frame104 a may have flanges around ⅛ in. wide. Panel 102 may be of eitherclear plastic or of glass. If of glass, it may be around 0.050 in.thick. Preload springs 109 may each be a round steel wire, 0.029 in. indiameter, and 0.080 in. longer than the matching side of panel 102. Inorder to adopt the correct straight form when assembled, each of springs109 may be given an unloaded curvature, which from a nil value at thespring's ends, increases linearly towards the center of the spring whereit is attached to the panel 102.

[0094] Lateral stiffening means 108 may comprise, for example, apolyester or polyimide film, 0.001 to 0.002 in. thick, with acrylicadhesive on the under surface in two areas where attachment is desired.The first such adhesive area 118 lies along the outer portion of 108beyond the dashed line, which portion folds down over the verticalflanges of frame 104 a. The second adhesive area 119 lies in a stripabout {fraction (1/16)} in. wide around the inner edge of 108. This areaadheres to touch surface 103 a slightly in from the edge of panel 102.The stress in lateral stiffening means 108, when bent along the dashedline, may be relieved, and lateral stiffening means 108 may thereby begiven a proper final contour, by a simple thermoforming operation. Thismay be performed either before or after assembly. The excess material atthe external corners of lateral stiffening means 108 may be folded alongthe diagonal, and laid over to the side against the vertical flange ofthe frame 104 a. The suitable breadth of the freely flexing region 120of lateral stiffening means 108 depends upon its own stiffness, upon thestiffness of panel 102, and upon the accuracy required. It may, forexample, be in the range of 0.060 to 0.120 in. It should be appreciatedthat the particular embodiment of the lateral stiffening means 108depicted in FIG. 1A is provided merely for purposes of example and doesnot constitute a limitation of the present invention. Rather, lateralstiffening means 108 may include any structure or structures that limitlateral movement of the panel 102 in response to touch forces.

[0095] In environments where accurate touch location is required on amoving or shaking display, accelerometers 115 a-b may be employed.Accelerometers 115 a-b may be rectangles of stainless or spring steelshim stock 1 mil thick, 0.120 in. wide, and 0.250 in long, plated forsolderability. In the embodiment depicted, accelerometers 115 aresoldered to lands 116, so that they carry over lands 117 as simplecantilevers, with capacitive gaps of about 2 mils. Any number ofaccelerometers may be used. For example, as shown in FIG. 1A, the twoaccelerometers 115 are symmetrically positioned on opposing sides andare connected in parallel. The resulting single channel of Z-axisacceleration may then be measured capacitively, and the results appliedto correct the force sensor channels as taught in Roberts U.S. Pat. No.5,563,632. Alternatively, three or four accelerometers driving separatesensing channels could be used, for example, to encode X and Yrotational accelerations, as well as the typically larger accelerationof Z displacement. Since the magnitude of correction required isgenerally modest, however, such refinement may not be necessary inparticular embodiments. Where one accelerometer suffices, it may also beplaced externally to module 101, such as on an accompanying applicationcircuit board. Such mounting may be parallel to the touch plane, and maybe centered approximately under the centroid of the touch surface. Aswith the principal elements of the force sensors, the accelerometerelements may be constructed in variations with other shape thanrectangular. They may be manufactured and assembled by many of the sametechniques as may be applied to the force sensors.

[0096] Since panel 102 is not secured via the force sensor or thepreload springs 109 in the embodiment depicted in FIG. 1A, lateralstiffening and restraint means 108 is employed both in its lateralrestraint aspect to maintain basic geometry, and in its lateralstiffening aspect to define dynamic lateral stiffness. Note, however,that lateral softening means 107 may be used even though panel 102 hasthe potential to slide by tiny amounts with respect to the sensorsbeneath. Preload forces, in addition to the touch force itself, maycreate sufficient friction to prevent any plausible tangential forcefrom causing such sliding during a normal touch. It is, therefore, theratio of the lateral stiffness of lateral stiffening means 108 to thatof the sensor assemblies only in the differential sense for small forcesthat cause no sliding which determines the path taken by tangentialtouch forces.

[0097] Although lateral stiffening means 108 is depicted in FIGS. 1A-1Bas a single piece of material, this is simply an example and does notconstitute a limitation of the present invention. For example, lateralstiffening means 108 may be assembled with 4 tape segments, butted oroverlapped in any of various ways at the corners. Alternatively, lateralstiffening means 108 may be, for example, a single sheet of transparentfilm, attached with an optically clear adhesive over the full interiorarea of touch surface 103 a. Lateral softening means 107 may include athin layer of a tough but soft elastomer, such as natural rubber.However, the simpler choice of soft acrylic adhesive has provensufficiently tough and compliant, in spite of being somewhat thinned inthe bearing area when the foil is only 0.0015 in. thick. Panel 102 maybe detailed at its edges, especially if made of plastic. For instance,holes parallel to the surface near the corners of the panel 102 mayretain angled preload spring ends, with hooks bent inward from frame 104a to hold the preload springs at their centers.

[0098]FIG. 2 presents touch overlay module 101 as it might be employedwithin a typical application device 201. Application enclosure 202includes bezel 203, carrying alignment feature 204 on its inner surface.Alignment feature 204 may, for example, be continuous, comprise periodicisolated protrusions, or comprise the ends of periodic stiffening ribs.In addition to touch overlay module 101, enclosure 202 contains LCDdisplay module 205, and application electronics 206. LCD 205 andelectronics 206 may be retained and positioned by standoffs as depictedhere for diagrammatic simplicity, or by engagement with molded detailsin enclosure 202. Touch module 101 may be retained, centered, andaligned with respect to the display surface of LCD module 205 by thepressure of bezel 203, in conjunction with feature 204 and the rigidsupport provided by LCD 205. When so retained, upon opening enclosure202, touch module 101, and perhaps the other internal components, may befreely separated. Alternatively, touch module 101 may be permanently orsemi-permanently fastened to LCD module 205 by such means as cement, oracrylic transfer adhesive, applied between frame 104 a and the surfaceof LCD 205. In this instance, feature 204 may be omitted, or may beemployed to better center the visual opening of bezel 203 by slightlyflexing the sides of enclosure 202.

[0099] The horizontal flanges of frame 104 a may receive support fromLCD module 205 by engaging either portions of the bare LCD glass,portions of the polarizer covering that glass, or portions of thepartial metal enclosure which typically wraps around the edges of LCDmodule 205. The highest surface encountered by frame 104 a willdetermine the source of support. The entire horizontal flange width offrame 104 a need not be engaged to provide satisfactory support, buttouch module 101 and frame 104 a may be sized such that engagementoccurs in the same plane around all, or nearly all, of the periphery oftouch overlay module 101. Small gaps in the support of frame 104 a aretolerable, but large gaps in support along the length of 104 a arepreferably, but not necessarily, avoided.

[0100] Note that the application of touch module 101 to the surface ofLCD module 205 generates gap 207. Some space (represented by gap 207)may be required for proper operation of touch module 101 so thatvertical displacements of panel 102 created in normal touch operation donot transfer forces by contact of panel 102 to LCD 205. Gap 207 may alsobe provided because of the fact that pressure applied to the surface ofan LCD module often results in unpleasant visual effects, due todisplacement of the image-forming fluids within the LCD. Finally,routine or heavy compression of the LCD surface may lead to damage,called “bruising”. Avoidance of such bruising may require a larger sizeof gap 207 than that used to satisfy the previously statedconsiderations.

[0101] If, however, the size of gap 207 as otherwise implied by theconstruction of touch module 101 is greater than desired, simplevariations of the embodiment depicted in FIG. 2 may be used to reducethe size of gap 207. In particular, a ledge or step in the back surfaceof panel 102 around its edge may be used to engage the force sensors attheir usual height, and provide clearance from frame 104 a, whilelowering the back surface of panel 102 over the display area of module205, thus narrowing gap 207. Touch surface 103 a may be left in theoriginal plane, thus occasioning greater thickness of panel 102 over thebulk of its area. Alternatively, touch surface 103 a may also be loweredsomewhat, and the overall height of module 101 thereby reduced. This ismade possible by the fact that the strength and stiffness of panel 102are related principally to the central portion of its area.

[0102] In a second embodiment of the invention, a force sensing touchlocation device is provided in which a surface of an LCD—rather than anoverlay panel (such as the overlay panel 102 shown in FIG. 1A)—serves asthe touch surface. For example, the actual display panel of an LCDassembly may replace the overlay panel 102 in the touch sensitivetransparent overlay module 101 shown in FIGS. 1A-1B. The display paneland possibly other internal components of the LCD assembly may then besupported by principal elements 106 in conjunction with lateralstiffening means 108. The force sensors based upon principal elements106 may thus be displaced considerably farther from the touch surface insuch an integrated touch LCD than in the transparent overlay module 101shown in FIG. 1A; however, the combined use of lateral stiffening means108 with lateral softening means 107 may be used to prevent theintroduction of tangential force errors.

[0103] As compared to the transparent overlay module 101, the touch LCDembodiment described above may benefit from improved optics, reducedoverall thickness, and reduced parallax. Improved optics resultprimarily from removing two of the three solid/air boundariespotentially requiring antiglare treatment. Reduced thickness may resultfrom eliminating gap 207 and merging of panel 102 with the top-glass ofthe LCD display to form a single glass layer of less aggregatethickness. Since these thickness reductions move the touch surfacecloser to the image-forming layer of the LCD, there is also a reductionin touch parallax.

[0104] Although, as previously stated, many LCDs are not appropriate fordirect application of touch, some are; and the designs of others may bealtered for direct application of touch in combination with the secondembodiment of the invention described above. Such alterations mayinclude, for example, a slight thickening of the LCD front glass.

[0105] Referring to FIG. 3, a self-contained, touch-enabled LCD module305 is shown according to the second embodiment of the invention. Thedifferences between touch LCD 305 and touch module 101 are bestexemplified in the cross-sectional diagram of FIG. 3, which alsoexhibits a typical containing application device 301.

[0106] Touch LCD 305 comprises frame 104 b, LCD electronics board 304,light diffuser 303, LCD display panel 302, principal elements 106,lateral softening means 107, and lateral stiffening means 108.Furthermore, preload springs similar in function to springs 109 are alsopresent, but do not show in the plane of section. Frame 104 b does notrequire a clear visual opening and so may close across the back of touchLCD 305, shielding, stiffening, and protecting it, and in other wayssubsuming some of the functions of a conventional LCD module frame.Frame 104 b, though still of thin material, here has substantiallygreater section depth than frame 104 a, and so does not include supportfrom behind, continuously or nearly continuously around its periphery,as frame 104 a does in module 101. A separate interconnect 105 is nolonger present, as its function is subsumed by LCD electronics board304. Board 304 is firmly supported against frame 104 b in the immediatevicinity of each of the principal elements 106. However, depending uponthe thickness of board 304, the firm support may not require bondingsufficient to stiffen board 304 under principal elements 106. The goalmust be to achieve sufficient net stiffness under principal elements 106that the end constraint, in this sensor embodiment, is essentially aclamped end constraint. In particular, the residual elasticity of theend constraint should be sufficiently small and/or reproducible that thebehavior of the force sensor is not rendered unpredictable.

[0107] In the variation depicted in FIG. 3, diffuser 303 and displaypanel 302 interlock, or are otherwise so attached, as to travel togetherfor purposes of positioning and force transmission. They aresupported—in a manner similar to panel 102 of module 101—by lateralsoftening means 107, coupling to bearings 121 of principal elements 106;and by lateral stiffening means 108.

[0108] Note that diffuser 303 is depicted with shallow bosses extendingdownward to establish contact with the force sensors. This is becausethe force sensing assemblies will generally be thinner than the thickestcomponents mounted to board 304. In other variations, the diffuser 303may be carried with board 304 and move independently of display panel302. Perpendicular forces applied to panel 302 are then transmitted backto the force sensors through columns, bosses, or tabs extending between.These roughly columnar structures may have sufficient flexibility inboth transverse directions to perform the same function as lateralsoftening means 107, obviating the need to entrain a thin layer of softmaterial as previously depicted. Such columnar structures may be moldedas part of the same component comprising diffuser 303, being softlyconnected thereto by thin molded connections.

[0109] Display panel 302 may connect to electronics 304 with either flexcable, or a sufficiently compliant elastomeric connector. If theconnection is hard-docked, as with screws, a cantilever tab may berouted into the edge or interior of the PC board of 304 to carry theconnection with sufficient perpendicular compliance.

[0110] Various embodiments of the invention employ no permanentconnection between the force sensing assemblies and the floatedstructures they support, whether overlay plate or display components.This simplifies assembly, relaxes requirements for precision anddimensional stability, and provides a simple means whereby the forcesensors may be protected from unwanted rotational sensitivities. In suchembodiments of the invention, provision may be made to establish astatic perpendicular preload force to keep the floated components firmlyseated against the force sensors during all ordinary conditions ofoperation.

[0111] In one embodiment of the invention, the preload means applysufficient total preload force, are possessed of a sufficiently lowspring constant, do not provide unwanted lateral stiffeningsignificantly removed from the plane of touch, and are coupled to thefloated components with sufficient symmetry to preload the sensorsmore-or-less equally.

[0112] In various embodiments, a minimum sufficient preload force may beestablished by factors including but not limited to the following. If itis desired that the touch apparatus operate in any orientation, a totalpreload force may be provided that exceeds the weight of the floatedoverlay plate or display components. In the case of large, staticallymounted displays, this may be the main consideration. In other cases,other total preload forces may be provided if particular resistance tovibration and/or enclosure torsion is desired. In automotiveapplications, for instance, the need to avoid buzzing under at leastseveral g's of vibration may lead to use of a total preload force of atleast several times the floated weight. In all applications, there isthe potential for unsymmetrical loading, as may occur when theapplication enclosure is seated against an uneven surface. This can leadto torsion extending to frame 104 a, such that the corners of frame 104a no longer lie in a common plane.

[0113] Modest preload forces prevent torsional problems with touchmodule 101. This is due to the relative flexibility of plate 102—whichis generally made as thin as possible—and to the stiffness of theunderlying LCD. Greater preload forces, and/or a surrounding structuremore resistant to torsion may be used with touch LCD 305.

[0114] In one embodiment, the preload force changes very little as afunction of ordinary touch displacements, in order that essentially allof the perpendicular force change occasioned by a touch may pass throughthe sensor assemblies. Thus, the preload force may be applied by elasticmeans which, in use, are deflected a long distance from their unloadedstate. The “long distance” in question is considered in comparison tothe distance through which the preload force deflects the common pathshared by both the preload force and perpendicular touch forces. In oneembodiment, each of the preload springs 109 of module 101 applies atotal force of about 1 lb. when its ends have been flexed through theapproximately one inch displacement required to place them in assembledposition. For example, a touch close to the location at which the spring109 is attached by cement 110 shares the maximum common path with thepreload force—conversely, it tends to generate the greatest flex inpreload spring 109. For a one pound touch force, the deflectiongenerated at the location of cement 110 is not more than a fewthousandths of an inch, the great bulk of which occurs in panel 102itself, rather than in principal elements 106. Since the preload forceis a roughly linear function of preload spring deflection, it can beseen that well under 1 percent of the perpendicular touch force isdiverted through springs 109, and therefore “not seen” at the forcesensors.

[0115] Since the ends of springs 109 press upward against the innersurfaces of holes 112 at points very close to the plane of touch, it isimmaterial that springs 109 may provide significant additional lateralstiffness against displacements parallel to their length. Otherembodiments of the preload springs 109, however, with an end or endsretained significantly out of the plane of touch, might include someancillary lateral softening means.

[0116] Alternatively, in other embodiments, preload spring may beapplied along all four edges of an overlay or other touch surfacestructure, and by appropriate attachment of their ends, serve also aseither lateral stiffening means or lateral restraint means. Furthermore,such springs may be located wholly or in part below the touch surface.With an appropriate shallow sigmoid shape, and supporting ends attachedsomewhat below centers affixed to the touch surface structure, suchsprings may further comprise a lateral stiffening means in accordancewith an angled stiffness structure, as described in the co-pendingapplication entitled “Tangential Force Control in a Touch LocationDevice.”

[0117] Touch LCD 305 may be preloaded with a design identical to that oftouch module 101. Free access to areas behind the display panel 302,however, creates other opportunities for locating the preload means. Asingle spring, for instance, might be attached to the back of the LCDpanel 302 near its center. A spring wire, having the assembled shape ofa “Z”, might attach at its ends to the frame sides, and at its center tothe back of the LCD panel 302. A nearly closed “C” shape might connectat its ends between the opposed centers of the frame back and of thefloated assembly. Many other variations will be apparent to those ofordinary skill in the art. Note that the preload spring attachments maybe well removed from the plane of touch; therefore the shape of thespring may allow relatively soft flexure in all directions, in whichcase additional lateral softening may not be used.

[0118] Note that preload may be accomplished with a larger number ofsmaller elastic devices. For example, such elastic devices may attach tothe floated components at points adjacent to each sensor. In oneembodiment, the perpendicular deflection of the sensor assembly issmaller than the deflection that will occur in the overlay or LCD panel302 at points far from support. Thus, springs located very close to thesensors may have smaller unloaded displacements, less assembled energystorage, and substantially smaller size, and yet still divertinsignificant touch force. In the situation just described, where thesensors are stiff compared to the touch surface, a preload spring nearone sensor will do little to load others. Therefore, it may beadvantageous to use one preload spring per sensor.

[0119] An application bezel, such as application bezel 203, typicallyapplies forces to a touch module such as touch module 101 or a displaymodule such as display module 305. These will include static forcesassociated with assembly and seal maintenance, and variable forces fromhandling. A force-based touch system should be designed such thatoperation is not disturbed by these forces. In various embodiments ofthe present invention, components such as frames 104 a and 104 b receiveand transmit these forces. For example, frame 104 a may be provided withan elevated lip; that is, a vertical flange which rises above the levelof touch surface 103 by a small amount. This facilitates use of anapplication bezel of simple design, that may have a flat and parallelundersurface, without danger of touching the overlay panel 102 (or,similarly, the floated LCD panel 302 in FIG. 3). In application, bezelforces applied to touch module 101 are transmitted directly to thesurface below, which may be a very stiff LCD module. Thus by “borrowing”the stiffness of the surface below, frame 104 a resists significantdeflections. The bezel forces of greatest concern are predominantlyperpendicular. Thus the greater section depth of frame 104 b also allowsthe bezel forces to be successfully resisted in touch LCD 305 (FIG. 3),in spite of the use of thin material.

[0120] The thinness of the vertical legs of frames 104 a and 104 bmaximizes the active touch area in relationship to the overall moduledimensions. In touch LCD 305, for example, rearward placement of theforce sensors, combined with the thinness of the vertical leg of frame104 b, allows the lateral dimensions of touch LCD 305 to be scarcelygreater than those of an LCD with the same image size not equipped fortouch. Since frame 104 b replaces a partial metal enclosure normallypresent, increase of width is limited to the introduction of a smallclearance gap, plus any differential in material thickness. Since touchLCD 305 also avoids much or all of the increase in thickness usuallyassociated with touch input, touch LCD 305 is of particular benefit inportable, or other space-constrained, applications.

[0121] Thus, in addition to other functions, vertical legs of frame 104a and 104 b are seen to comprise application bezel support members.

[0122] In other variations of the invention, an additional applicationbezel support member may be provided, that both closely invests theforce-sensitive structure, and that transmits application bezel forcesto support behind. For instance, in one variation, a continuous rib orflange member may be molded into the application bezel. This flangemember may extend perpendicularly downward from the undersurface of theapplication bezel, emerging from the lateral body of the applicationbezel along a line spaced slightly in from the visible edge of the bezelopening, and resting along its lower edge along the LCD display or otherstiff support surface beneath. The height of the flange member is suchas to provide necessary clearance between any inwardly protrudingextension of the application bezel and force sensitive structures. Theflange member may be fully continuous; however, it may also beinterrupted into a sequence of segments or a row of bosses, closelyenough spaced to “borrow” the necessary stiffness from below.

[0123] In another variation, an additional application bezel supportmember may comprise a vertical leg of a metal stamping coupled to, orpart of, an LCD or other display assembly, but distinct from thevertical leg of frame 104 a or its equivalent, while wrapping around andclosely investing it. In yet another variation frame 104 may take theform of a “U” channel, with the interconnect and force sensors attacheddirectly to the display surface just inside this channel. The innervertical leg may then provide support for a lateral stiffening andrestraint means, seal, and preload means, while the outer vertical legcomprises an application bezel support member.

[0124] In yet another variation of the invention, an additionalapplication bezel support member may, while remaining laterally thin, beextended perpendicularly so as to closely invest an entireforce-sensitive display structure or more, thereby achieving from depthof section greater stiffness against flexure from perpendicular bezelforces. Such member may then receive support for such forces fromlocalized attachments to structures behind, or from other structures notconstituting a continuous stiff surface of support.

[0125] In various embodiments of the present invention, the applicationbezel support member of the invention comprises a path for bezel supportthat closely invests force-sensitive structures; cantilevered supportfrom the outer edges of an application enclosure is thus avoided, anddisturbance to force-sensitive structures is minimized. A novelopportunity for forming an overall liquid and/or dust seal may also bethus obtained.

[0126] The lip of the vertical leg of frame 104 a provides a lineagainst which the application bezel 203 may achieve a dust and/or liquidseal, and also provides a convenient point of attachment for continuinga flexible liquid and dust seal from the frame 104 a to the touchsurface 103 a. By providing a separation of the sealing function into aninternal flexible seal and an external application seal, variousembodiments of the invention simplify application assembly. The verticalframe leg also provides a point of attachment for a lateral stiffeningmeans (such as lateral stiffening means 108) which is close to the planeof touch. While the lateral stiffening means, lateral support means, andthe sealing means are embodied within the same physical element in theparticular embodiment depicted in FIGS. 1A-1B, FIG. 2, and FIG. 3, thisneed not be the case. In some applications, for example, there may beadvantage in confining the lateral stiffening means and/or lateralrestraint means to the vicinity of the sensors, where less verticalflexure is encountered, while distributing a thinner seal film aroundthe entire periphery.

[0127] Various embodiments of the present invention advantageouslyreduce the introduction of touch location errors by tangential forces.For example, referring to FIG. 4, touch surface 103 (which may, forexample, be the touch surface 103 a shown in FIG. 2 or the touch surface103 b shown in FIG. 3) resides upon floated structure 401, which mayrepresent, for example an overlay (such as overlay panel 102 shown inFIG. 1A) or display unit (such as LCD panel 302 in FIG. 3). A finger402, applies a touch force comprising tangential component 403 andperpendicular component 404. Structure 401 is supported by a lateralstiffening means 405, and by force sensors 407 through lateral softeningmeans 406. Receiving all forces is surrounding structure 408. Tangentialcomponent 403 of the touch force applied by the finger 402 generatesreactions 409, and perpendicular component 404 of the touch forceapplied by the finger 402 generates reactions 410 a and 410 b. Due tothe construction and positioning of lateral stiffening means 405, thecombination of component 403 and reactions 409 generate no net moment.In the absence of such extraneous moments, then, the partitioning of thereaction to perpendicular component 404 between 410 a and 410 baccurately locates the touch position in accordance with force andmoment equations that are well-known to those of ordinary skill in theart.

[0128] Although lateral stiffening means 405, force sensors 407, lateralsoftening means 406, and surrounding structure 408 are illustrated inFIG. 4 in generalized form, it should be appreciated that these elementsmay be implemented, for example, as shown in FIG. 1A, FIG. 2, and FIG.3. For example, lateral stiffening means 405 may be lateral stiffeningmeans 108, force sensors 407 may be the force sensors shown in FIG. 1A,lateral softening means 406 may be lateral softening means 107, andsurrounding structure 408 may be enclosure 202 and/or frame 104 a or 104b. Note also that lateral softening means 107 may be provided belowsensors 407, rather than above as shown, and also provide the desiredfunction. Further, if the lateral stiffness of the force path throughstructure 401, sensors 407, and supporting structure 408 is low enoughcompared to that of the force path passing through lateral stiffeningmeans 405, then lateral softening means 407 may be omitted.

[0129] Lateral stiffening means 405 is in part so named because it restswhere a void might well exist in a conventional force-based touchdevice, while lateral softening means 406 is in part so named because itis inserted where a rigid coupling typically exists in conventionalforce-based touch devices. Note that in both cases, though, a couplingmay be desired which is much stiffer to forces applied in one directionthan to another at right angles. Columns, beams, plates, and membranesof high aspect ratio, for example, have this property, as do high aspectlayers of elastomer trapped between rigid flat surfaces. Classicalbearings do also, of course, but here it is better, as well as simpler,to avoid rubbing surfaces that may exhibit stiction at small forcelevels.

[0130] Some additional aspects should be noted which are not showndirectly in FIG. 4. Lateral stiffening means 405 may also be presentalong the edges above and below the plane of the FIG. 4. In variousembodiments of the invention, reaction forces 409 are developedprimarily through shear in these other portions of lateral stiffeningmeans 405.

[0131]FIGS. 5A, 5B, and SC illustrate one embodiment of the lateralstiffening means 405. Generalized floating structure 401 a, which mayrepresent an overlay (such as overlay panel 102 shown in FIG. 1A) ordisplay unit (such as LCD panel 302 in FIG. 3), receives perpendicularsupport from generalized force sensor 407 through lateral softeningmeans 501, portrayed in this variation as an elastomeric sheet. Lateralstiffening means 502 is a sheet of material, with its freely flexingregion intended to rest as close as possible to the plane of touch.Lateral stiffening means 502 may be carried around the full periphery of401 a, or may be confined to certain regions, such as those near thesensor mountings. There are two independent degrees of tangential force;one directed along the left/right axes of FIGS. 5A-5C, and tending toplace the portion of lateral stiffening means 502 visible in thesesections into tension or compression, and another perpendicular to theplane of FIGS. 5A-5C, and tending to place the portions of lateralstiffening means 502 visible in these sections into shear. If lateralstiffening means 502 is kept essentially flat, both degrees areeffectively resisted by all portions of lateral stiffening means 502.For most of the materials of which lateral stiffening means 502 might becomposed, the ratio of Young's modulus to the modulus of rigidity issuch that about 3 to 4 times as much stiffening will come from portionsof lateral stiffening means 502 in tension or compression as from equallengths in shear.

[0132] Referring to FIG. 5B, perpendicular force 503 may cause aperpendicular deflection of touch surface 103 through distance 506, suchthat the flexing portion of lateral stiffening means 502 becomes tiltedand stretched. This distance 506 may be particularly large at pointsmidway between the support offered by the sensors, as is depicted inthis cross-section. Tension in lateral stiffening means 502 rises as thesquare of distance 506. Due to the tilting of lateral stiffening means502, this tension has a vertical component 504, which becomes part ofthe balancing reaction to applied force 503. This diminishes thereaction component 505, passing through the out-of-section sensors, tobelow the expected value, causing some error.

[0133]FIG. 5C depicts a situation in which the flexing portion oflateral stiffening means 502 is tilted in the absence of perpendicularload. Distance 510 may represent, for example, either an intentionallyraised lip of frame 104, or the effect of component and assemblytolerances. Tangential force 507 causes compression in lateralstiffening means 502. Since this compression is tilted, it contains aperpendicular component balancing reaction 509, in addition to atangential component that balances the tangential force 507. A similarsituation in tension occurs along the opposing edge. Error force 509 andits equal but opposite counterpart acting upon sensors along theopposing edge, together represent a substantial moment generated inreaction to tangential force 507. This “jamming” effect representsanother characteristic of the configurations depicted in FIGS. 5A-5C.

[0134]FIG. 6 depicts another lateral stiffening means 601, which isprovided everywhere with a modest contour. Because lateral stiffeningmeans 601 is compliant vertically (i.e., in a direction substantiallynormal to the touch surface 103), this contour allows surface 103 to bedeflected substantially without placing lateral stiffening means 601into tension. This improves the range of touch forces which may belocated accurately, especially for touches near the edge betweensensors. The contour of lateral stiffening means 601 also greatlydecreases the lateral stiffening effect in tension and compression.Since the lateral stiffness provided by the sides of lateral stiffeningmeans 601 in shear may still be made sufficient, however, this isadvantageous in greatly decreasing error from imperfections which haveeffect selectively through the tension and/or compression of the lateralstiffening means (referred to herein as the “jamming effect”).

[0135] The structure of lateral stiffening means 601, and of othersdiscussed here, may also be employed as lateral restraint means. In suchuse, contouring conveys similar benefits with regard to increasing theperpendicular range over which perpendicular stiffness is slight, whileretaining a high ratio of lateral to perpendicular stiffness throughout.

[0136] Floating structure 401b is depicted with beveled edge 602. Thisallows the force sensors and the lateral stiffening means 601 to sharethe same narrow border width, while preserving clearance for the flexingportion of the latter. Application bezel 203 is depicted with additionalfeature 604 intended to guarantee clearance between the bezel 203 andboth lateral stiffening means 601 and surface 103. Bezel 203 is depictedas carrying fully over the border structures, both to conceal themcosmetically, and to protect lateral stiffening means 601 from damage.

[0137] An additional point may be noted with regard to the contour oflateral stiffening means 601. The elastic axis of rotation for lateralstiffening means 601 in shear lies at the level of dashed line 603. Forroughly circular contour, the offset of dashed line 603 from the planeof touch is approximately twice the maximum offset of lateral stiffeningmeans 601 itself. If the contour of lateral stiffening means 601 werethat of a shallow “V,” dashed line 603 would lie at the level of itspoint. Since the plane of accuracy lies at the level of dashed line 603,tangential force rejection is not perfect; it is, however, stillsubstantial.

[0138] FIGS. 7A-7C depict additional variations 108 a-c of the lateralstiffening means 108, as may be applied, for example, to the first andsecond embodiments depicted in FIGS. 1A-1B, FIG. 2, and FIG. 3. In thesevariations, frame 104 is depicted with an intentional elevation, or lip,which may rise 0.020 in. above touch surface 103. Lateral stiffeningmeans 108 a also acts as a seal and is provided with a fairly abrupt“dog leg” contour 701 a. Most of the flexing region of 108 a is backedup by overlay 102. This portion achieves the advantage of becoming quiteresistant to damage, and need not necessarily be covered by theapplication bezel 203 a. It should be appreciated that in otherembodiments, lateral stiffening means 108 a may not provide a sealbetween frame 104 a and touch surface 103.

[0139] In FIG. 7A, contour 701 a is placed close to the point 702 atwhich lateral stiffening means 108 a attaches to surface 103. Bezel 203a is of minimal width. Lateral stiffening means 108 a may be opaque, andof a color suitable for a visible detail of the border. Note that thereis little or no exposed cavity under the bezel 203 a where contaminationmay collect, so that this arrangement may be particularly suitable fordirty environments. In FIG. 7B, contour 701 b is placed close to the lipof frame 104. Bezel 203 b is depicted concealing the border structures.Lateral stiffening means 108 a and 108 b in FIGS. 7A and 7B,respectively, may be applied as, for example either four separate tapes,or as a single die cut piece.

[0140] For the dog-leg lateral stiffening means 108 a-b of FIGS. 7A-7B,the elastic axes 603 for rotation in reaction to shear lie atapproximately the average height of the flexing portion of the lateralstiffening means above touch surface 103. The resulting plane ofaccuracy may be sufficiently close to the touch plane for many purposes.Note, however, that any residual jamming effect tends to put the planeof accuracy below the touch surface 103, whereas the axes 603 here lieabove it. Thus by adjusting the position of contour 701 and/or the lipheight, the two opposing effects may be adjusted to cancel out. Thisconstitutes one example of a lateral stiffening means that createstangential reaction forces much more closely confined to the plane oftouch than is the lateral stiffening means itself.

[0141] In FIG. 7C, lateral stiffening means 108 c comprises atransparent film which passes over the entire touch surface 103. Thearea of lateral stiffening means 108 c interior to the point ofattachment 702 is fastened with optical adhesive. If bezel 203 a isminimal as shown, and if floating structure 401 is otherwisetransparent, it may be cosmetically advantageous to coat the upper orlower surface of floating structure 401 along the edges with opaquematerial (so as to conceal sensors and other edge structures from userview). If floating structure 401 is a glass overlay or fragmentabledisplay, lateral stiffening means 108 c provides an advantageous safetyeffect in case of breakage. Since surface 103 is of uniform opticalquality right up to the point of attachment 702, this point may now beplaced farther inward without increasing the border width. Since thefull border width is now available for the flexing portion of 108 c, theadvantage is gained that the lateral stiffening means 108 c may now bemade thicker, and therefore tougher, without giving it excessiveperpendicular stiffness.

[0142] Turning to FIG. 8, molded plastic bezel insert 801 carriestransparent protective film 802. Flange 803 on insert 801 engages slot804 in application bezel 203 b. Together, insert 801, film 802, andbezel 203 b provide a liquid/dust seal. Film 802 also protects the uppersurface of structure 401 from scratches, especially if it is a plasticoverlay or an LCD polarizer film. If 401 is a bare glass overlay, film802 provides some protection from shards in case of breakage. Thecombination of insert 801 with protective film 802 constitute a parteasily replaced in the field. Tiny holes 805 are present at the centerof each side, and provide purchase for a needle or pointed tool to drawthe insert inward out of slot 804. Flange 803 and slot 804 are engagedmaximally at the mid sides, but taper to negligible engagement at thecorners to facilitate replacement.

[0143] Touch pressure brings film 802 into firm contact with the surfaceof 401 under the point of contact, allowing the touch module below tolocate the point accurately. Film 802 may be made quite thick, sinceperpendicular force transmitted to its attachment at 801 does notgenerate a reaction force passed to 401. That is, there is no analog tothe problem depicted in FIG. 5B. Lateral stiffening/restraint means 806is also provided, but this no longer need perform a combined sealfunction, and may be implemented in a wide range variations.

[0144] Turning to FIGS. 9A-9B, a larger sensor according to anotherembodiment of the invention is depicted. Principal element 106 b is madefrom spring steel strap ¼ inch wide and 10 mils thick. This is cut to alength of ¾ in. and pressed in a die to the shape shown. The capacitivegap is 5 mils, but has been drawn with some exaggeration for clarity.The free span of principal element 106 b is 550 mils, the central 300mils of which are opposed by land 114. A substantially planar supportsurface is found on the epoxy glass PC board 901, which is only slightlylarger than principal element 106 b. Discrete wiring 105 b providesinterconnection. PC board 901 is mounted against underlying support 408with segments of acrylic tape 902, which also constitute a lateralsoftening means. PC board 901 is of sufficient stiffness that lateralsoftening means may be placed thereunder. This configuration has theadvantage that should support 408 flex, its curvature is very poorlytransmitted to board 901, thus preventing enclosure forces fromdisturbing force readings. Pivoted force bearing 121 b is in the form ofa ridge, and suffices to fix sensor sensitivity, while providing goodstrength against extreme overloads. Unloaded capacitance is about threepicofarads, and the bottoming-out force is between four and five pounds.

[0145] Although the use of different materials may require other choicesof dimensions, the principal element 106 b may be made from othermaterials, such as plastic with a electrically conductive coating.

[0146] Turning to FIGS. 10A-10B, a smaller sensor according to oneembodiment of the invention is depicted. Principal element 106 is cutfrom spring steel 6 mils thick. It is 120 mils wide and 230 mils long.Alternatively, principal element 106 may be of phosphor-bronze 8 milsthick, with the same length and breadth. The capacitive gap is 1 mil,formed by spacing the gap with a temporary shim while lands 113 arereflowed with solder. Alternatively, the solder may contain particles ofcontrolled size that act to space the principal element 106 from lands113.

[0147] Bearing dimple 121 may be created with a spring-loaded centerpunch while principal element 106 is pressed against an aluminumbacking. The free span of principal element 106 is 150 mils, the central86 mils of which are opposed by land 114. Unloaded capacitance is aboutthree picofarads, and the bottoming-out force is between three and fourpounds.

[0148] Other details of assembly are as described for the sensors shownin FIG. 1A.

[0149] Capacitive force sensors exhibit a change in capacitive reactanceas a function of a change in applied force. For the sensors of FIGS.9A-9B and 10A-10B, this change is substantially linear for smallerforces, where the relative gap change is small. With larger forces,however, the center of the capacitive region closes up while the edgesremain more widely spaced; this leads to a drop in reactance thatbecomes more rapid than linear. To increase the range of force sensingthat may be accomplished with high accuracy, compensation for theresponse characteristic just described may be accomplished in theprocessing of the sensor signal; alternatively, varied embodiments ofthe sensor of the invention may be provided which have an inherentlygreater range of linear reactance change.

[0150] Thus in another novel aspect of the invention, a capacitive forcesensor of nonuniform gap may provide improved linearity of measurementwith simple processing of the signal, even where one or more capacitorplates are flexing in response to applied force.

[0151] For example, FIG. 11 depicts a sensor 1100 with overalldimensions similar to those of the sensor of FIGS. 10A-10B. Principalelement 106c, however, has been provided with a slight bend ofcontrolled shape. Because this bend would otherwise be too subtle todepict with clarity, the vertical dimensions of the sensor 1100 areexaggerated tenfold in FIG. 11 with respect to the sensor's horizontaldimensions. The bend is such that the ends of element 106 c may attachto lands 113 with a minimal solder film, while the center provides amaximum capacitive gap (between point 1102 and the upper surface of land114) of about 1.5 mils.

[0152] There is a level of force that may be applied to coupling 121 cwhich is just sufficient to first bring element 106 c into contact withthe land 114. The tapering of the capacitive gap away from the exactcenter point 1102 of element 106 c may be so shaped that this contacttends to happen simultaneously at all points where element 106 c opposesland 114.

[0153] Such a nonuniform gap design may help to provide a force sensorwith optimal linearity. Call a general applied force “F”, and call theminimum force to bottom out the sensor “F_max”. Subject to theassumptions that the gap is thin compared to its lateral dimensions, andthat Hooke's law applies, the stated condition upon the gap shaperequires that the gap spacing be everywhere proportional to F_max−F.Each small region then adds to the total capacitance a contributionproportional to 1/(F max−F). This expression of the functionaldependence upon applied force is not itself a function of position, andso factors out of the area integral defining the total capacitance. Theoverall sensor capacitance thus varies in proportion to 1/(F max−F), andits capacitive reactance at a given frequency is proportional toF_max−F. This is, of course, the expected behavior for an ideal parallelplate capacitor spaced by an ideal spring. Thus a linear measure of theperpendicular force transmitted may be obtained by differencing thereactance before and during a touch, for the full range of gap closure.

[0154] Principal element 106 c is substantially rectangular and ofuniform thickness, and is mounted rigidly at its ends through lands 113to interconnect 105 or other support. Also, all deflections to beconsidered are small compared to the thickness of element 106 c.Therefore, perpendicular force applied to coupling 121 c will deflectelement 106 c in a pattern closely approximating that of a centrallyloaded uniform beam with clamped end constraint. This deflection patternmay be expressed as d·(3·x²−2·x³), where d is the maximum deflection,and x is the fractional position along element 106 c, measured from thelast clamped point 1101, where x=0, to the center of element 106 c atpoint 1102, where x=1. The curve from point 1102 to point 1103 thencontinues as the mirror image of this.

[0155] The desired shape for element 106 c in its unloaded condition is,therefore, the negative of this deflection pattern, extended with flatends for mounting. In cases where the end constraint has significantrotational flexibility, the correct shape for element 106 c may bederived from the stated deflection pattern by associating with point1101 a value of x that is somewhat larger than zero. In the limitingcase of simply supported ends, x=0.5 may be assigned to point 1101,while x=1 is still assigned to point 1102.

[0156] For convenience of exposition, the curve for element 106 c hasbeen defined here over the entire span between attachments at point 1101and point 1103. Only the area of element 106 c opposing the secondcapacitor plate (i.e., land 114) needs to follow this curve, however, solong as other regions do not bottom out before the capacitive areas do.

[0157] Although providing substantial improvement, this one-dimensionalanalysis is not fully precise, given that coupling 121 c approximates apoint feature, rather than a linear one as does bearing 121 b of FIGS.9A-9B. Further degrees of refinement, however, may be obtained asdesired through methods of analysis well known in the art, as well as byempirical means. Such methods may also be similarly employed tolinearize the reactance response of a wide range of other capacitiveforce sensor variations that fall within the scope of the invention.Such variations include, for example, complex outlines, nonuniformthickness, flexure in one capacitor plate or both, multiple areas ofsupport or single cantilevered support, etc. In all cases, the desiredeffect is achieved by shaping the surfaces of one or both capacitorplates to produce a gap that “bottoms out” simultaneously at all points.

[0158] Turning to FIGS. 12A-12D, additional outline and mountingarrangements of force sensor principal elements are shown according tovarious embodiments of the present invention. All of the elements shownin FIGS. 12A-12D may, for example, be made with uniform thickness.Principal elements 106 d, 106 e, and 106 f provide regions variouslynarrowed so as to concentrate flexure in areas 1203 a-c not serving ascapacitor plates. This reduces flexure in capacitive areas 1202 a-c,improving linearity of reactance change. Couplings 121 d-f receiveperpendicular force, which is passed to structures beyond via supportareas 1201 a-c. With the thicknesses of the principal elements 106 d-fbeing greater, for a given stiffness, than elements of similar sizewithout narrowed regions, clamped support of areas 1201 a-c may receiveless concentrated twisting stress. Conversely, the concentration offlexure into areas 1203 a-c means that simple support of areas 1201 a-cwill see greater rotation. Couplings 121 d-f may be elevated features asdescribed previously, elastic features as described below, or any othercoupling feature providing a defined path for entrance of the force tobe measured.

[0159] Referring to FIG. 12C, principal element 106 f is provided withthree areas of support 1201 c, whereas principal element 106 g (shown inFIG. 12D) is a simple cantilever with a single area of support 1201 d.Cantilevered element 106 g must, of course, receive clamped support inarea 1201 d; whereas the other elements 106 d-f may be adapted foreither simple or clamped support in areas 1201 a-c, respectively.

[0160] Turning to FIGS. 13A-13B, additional variations for thecross-sectional shape and thickness of a principal element of a forcesensor are shown according to embodiments of the present invention. Forexample, referring to FIG. 13A, a sensor 1300 is shown according to oneembodiment of the present invention. The vertical dimensions of thesensor 1300 (and the sensor 1310, shown in FIG. 13B) are exaggeratedapproximately tenfold in FIG. 13A with respect to the sensor'shorizontal dimensions. Principal element 106 h has relatively thinregions 1303 between mounting regions 1301 and capacitive region 1302.These may be produced from planar feedstock by a process such as, forinstance, coining. They may again serve to reduce the relative amount offlexure in capacitive area 1302, thereby improving linearity. Referringto FIG. 13B, principal element 106 i of sensor 1310 achieves a similarrelative stiffening of capacitive region 1302 by laminating thisportion. As depicted for principal element 106 h, a principal elementrelatively thicker in support regions 1301 may advantageously reducestress in the support attachments caused by the moments passing throughthem.

[0161] Referring to FIGS. 14A-14C, an embodiment of a sensor accordingto another embodiment of the present invention is depicted in which theprincipal element is simply supported, and in which the second elementis a discrete element of identical manufacture to the principal element.

[0162] More specifically, turning to FIG. 14A, principal element 106 j(shown in solid outline) may be 300 mils wide and may be stamped orphotoetched from beryllium-copper 15 mils thick. Tabs 1401 a-b engageplastic spacers 1402, allowing principal element 106 j to be assembledopposite another identically manufactured element 1403, which, flippedend-for-end with respect to 106 j, is inserted into the same pair ofspacers 1402.

[0163]FIG. 14B presents a side view of plastic spacer 1402. Rectangularholes 1404 a receive tabs 1401 a of one element (such as element 106 j),while rectangular hole 1404 b receives tab 1401 b of the opposingelement (such as element 1403). Elevations 1405, on the sides of thespacers 1402 away from the principal element 106 j, locate the forcesensor by engaging holes (not shown) in the support surface. Thus at oneend of the force sensor, the support surface corresponds to the plane of1406 a, and at the other, of 1406 b.

[0164]FIG. 14C presents a partial cross-section in which principalelement 106 j and element 1403 are employed as a force sensor in a touchlocation device. Spacers 1402 are employed above and below the plane ofsection, and seat against the immediate support surface provided byouter frame 104 c. Transparent touch overlay 1408 is secured within theinner frame 1407 by cement 1411. The combination is then supportedperpendicularly by plastic force transmission couplings 121 h, one ofwhich is associated with each sensor. Couplings 121 h may be press fitinto holes in inner frame 1407, which align over the centers of thesquare capacitive areas afforded by each of the principal elements 106 jemployed. Inner frame 1407 is supported laterally by combination sealand lateral restraint means 1409. Oversize clearance holes may beprovided in inner frame 1407, if necessary, to guarantee that there isno contact with the unused elevations 1405 that are on the surfaces ofspacers 1402 directed upward. Discrete wiring 1410 may connect to theupper surfaces of tabs 1401 by soldering or wire welding. Applicationbezel 1412 seats against lateral restraint means 1409 and frame 104 c.

[0165] When unloaded, principal element 106 j rests about 10 mils abovethe surface of non-flexing element 1403. Holes 1404 a-b are somewhatlarger at the surface of spacer 1402, and taper to minimal cross-sectionat its center, which cross-section just matches tabs 1401 a-b. Thus asforce is applied to coupling 121 h, principal element 106 j flexes as amember having simply-supported end constraint with minimal friction.

[0166] The arrangement of FIG. 14C offers a touch location device ofminimal thickness, but the inclusion of inner frame 1407 increasesborder width. The sensor is scalable to other, including smaller, sizes.

[0167] Since principal element 106 j may be located quite close to theplane of touch, special provisions for handling tangential forces may beomitted without significant adverse consequences. For instance, theaggregate lateral stiffness of lateral restraint means 1409 need notsubstantially exceed the aggregate lateral stiffness of the forcesensors and their couplings 121 h. Nevertheless, it should be noted thatlateral restraint means 1409 provides a novel means of lateral assemblyalignment having high perpendicular compliance.

[0168] We now consider sensors of a type made in accordance withembodiments of the invention where the principal element is made of aninsulating material with a conductively coated area or areas.

[0169] Turning to FIG. 15A, epoxy glass PC board 1501 includes a regioncomprising principal element 106 k. Principal element 106 k compriseslands 113 and 114, and such portions of the epoxy glass substrate asstore significant elastic energy associated with changes in thecapacitive gap.

[0170] As may be seen more clearly from cross sectional FIG. 15B, apredefined path carries applied force from touchable structure 401,through force-coupling elastomeric pad 121 i, upper capacitor plate1503, and spacing/connecting solder film 1505, to central region 1506 ofprincipal element 106 k. Central region 1506 is flanked by slots 1502,which serve both to increase and to relatively localize the flexure inthe PC substrate. From central region 1506, force passes both out andaround the ends of slots 1502, eventually reaching PC board supports1504. As force passes away from the immediate vicinity of the capacitivearea and the slots 1502, any additional flexure it produces ceases torelate to force-induced changes in the capacitive gap, and so is nolonger passing through the force sensor. If present, supports 1504placed close to the sensor may have some effect upon sensitivity andsymmetry of response. Such close supports may be given a symmetricaldisposition, such as that shown, not excessively close to central region1506. More remote supports may be placed in any pattern desired.

[0171] Elastomeric pad 121 i provides both lateral softening and adegree of rotational softening. As such, pad 121 i may serve as analternative to the combination of raised feature 121 and lateralsoftener 107 shown in FIG. 10B. Pad 121 i may be fastened adhesively tothe capacitor plate 1503 below, but not attached above. Structures abovemay then be aligned and preloaded shown as elsewhere herein.Alternatively, pad 121 i offers the possibility of maintaining alignmentand assembly through adhesive attachments both above and below.

[0172] The variation presented in FIG. 15C alters the force path, as itnow passes through the length of the upper capacitor plate 1503. Thisupper plate 1503 may now make a significant contribution to the elasticenergy storage associated with the capacitive gap; in which case, it isappropriate to view the upper plate 1503 as an additional principalelement 106 q,working in concert with lower principal element 106 m.Force from element 106 q through solder 1505 b into element 106 m,continues around slots 1502, into central region 1506, and thence tosupport 1504 b.

[0173] Thus, many variations on the capacitive force sensor of theinvention will be evident to one of ordinary skill in the art. Thesevariations may share certain features, such as:

[0174] Major components of the sensor may be substantially planar, andmay be manufactured from planar materials. This provides inexpensiveaccess to high-precision flat surfaces, and to surfaces that aredesigned to deviate from flat by slight but precisely controlledamounts. Sensors according to various embodiments of the invention mayinvolve one or more substantially planar principal elements. Thesereceive and pass on forces through a predefined path, and respond to thenormal component of such forces by a normal displacement of a capacitivesurface that they expose. The capacitive surface so exposed may itselfbe subject to some degree of flexure. Note that the point at which forceenters a principal element may be considered to be that point beyondwhich force transmitted may produce flexure directly affecting themeasured capacitive gap.

[0175] Sensors according to various embodiments of the invention mayhave a very small gap; for this reason, in part, they may be made smallin comparison with the containing touch location device. Thegap-defining mechanical path of such sensors is small compared to thedimensions of the touch location device; as a direct result, the gapsuffers only tiny error deflections due to device flexure. Furthermore,the small size of the gap-defining path may effectively provideadditional error reduction through local stiffening and/or structuralisolation.

[0176] To more precisely understand the meaning of the term“gap-defining path” as used herein, draw a curve through space thatoriginates at the center of one capacitive area and terminates at thecenter of the opposing capacitive area. Pass this curve entirely withinsolid material fully contributing to the mechanical coupling between thetwo opposing capacitive areas. The term “gap-defining path” refers tothe length of the shortest such curve.

[0177] In sensors according to various embodiments of the invention, theextent of the gap-defining path projected along a line normal to thesensor (referred to herein as the aggregate normal component of thegap-defining path) may be scarcely greater than the thickness of the gapitself. Since the sensor spring lies in the same plane as itscorresponding capacitive area (e.g., both are embodied in the principalelement 106), and is a continuation of the same planar material definingthe plane of that area, some means of directly spacing the width of thegap is all that may be required to construct the capacitor. In prior artdesigns of capacitive force sensors, wherein the normal component of thegap-defining path is substantially larger than the gap itself, the gapis effectively determined by the small difference of two larger numbers.This has previously limited the precision, stability, and economy withwhich a very small gap may be employed.

[0178] The precision with which the directly-spaced gaps of sensors ofvarious embodiments of the invention may be made allows for a capacitivegap of high aspect ratio. Width and length that are large compared tothe gap spacing itself allow an adequate absolute capacitance to bemaintained as the sensor is miniaturized.

[0179] In some embodiments, some original material may be removed fromregions of originally substantially planar materials. Thus, 1 or 2 milsof copper may be etched from between the support lands 113 andcounter-electrode land 114, to isolate them electrically. The surfacesof lands 113 and 114 remain highly coplanar, however. Thus, in spite ofthis, and similar operations that may be performed between thecapacitive and support areas of substantially planar principal elements106, which operations may superficially increase the normal component ofthe gap defining path, the end surfaces continue to afford the sameopportunity for establishing highly precise, directly-spaced gaps usingoffsets or spacing means of roughly the same perpendicular extent as thegap spacing itself.

[0180] Capacitive force sensor stiffness in the direction of measurementmay be inversely related to the gap width. Thus, sensors according tovarious embodiments of the invention provide very high stiffness,raising the resonant frequencies of the supported structure andimproving the performance of the unit housing the force sensor. Keepingsensor motions very small also reduces the problem of force transmissionon parasitic paths (those not passing through a sensor).

[0181] Some variations of the sensor of the invention further exploit aninterconnect, such as a PC board, to provide both a substantially planarsupport surface and coplanar second capacitor plate for a principalelement.

[0182] It is to be understood that although the invention has beendescribed above in terms of particular embodiments, the foregoingembodiments are provided as illustrative only, and do not limit ordefine the scope of the invention. Other embodiments are also within thescope of the present invention, which is defined by the scope of theclaims below.

What is claimed is:
 1. A force sensor for sensing a touch force appliedto a touch surface, the force sensor comprising: a first elementincluding an elastic element and a first capacitor plate having a firstcapacitive surface, the elastic element including at least part of thefirst capacitor plate; and a second element including a second capacitorplate opposed to the first capacitor plate; wherein transmission of atleast part of the touch force through the elastic element contributes toa change in capacitance between the first capacitor plate and the secondcapacitor plate.
 2. The force sensor of claim 1, wherein the firstelement is substantially planar.
 3. The force sensor of claim 1, whereinthe first capacitor plate and the elastic element are integral.
 4. Theforce sensor of claim 3, wherein the first capacitor plate and theelastic element are composed of the same substrate.
 5. The force sensorof claim 3, wherein the elastic element comprises an elevated feature ofthe first capacitor plate.
 6. The force sensor of claim 5, wherein theelevated feature is located at the elastic center of the first element.7. The force sensor of claim 1, further comprising force-receiving meansfor receiving at least part of the touch force into the first element.8. The force sensor of claim 7, wherein the force-receiving meanscomprises the elastic element.
 9. The force sensor of claim 7, whereinthe force-receiving means comprises a feature formed into the firstelement.
 10. The force sensor of claim 9, wherein the force-receivingmeans comprises an elevated feature of the first capacitor plate. 11.The force sensor of claim 7, wherein the touch surface is incommunication with a region of a surface of the force-receiving means,and wherein the touch surface tends to remain in contact with the regionof the surface of the force-receiving means when the position of thetouch surface changes with respect to the force-receiving means.
 12. Theforce sensor of claim 1, further comprising force transmission means fortransmitting at least part of the touch force to at least one structureother than the first element.
 13. The force sensor of claim 1: whereinthe second element comprises a planar support surface that includes aplurality of electrically conductive mechanical bearing contacts; andwherein at least portions of the first capacitor plate are in contactwith the plurality of mechanical bearing contacts to transmit forcethereto.
 14. The force sensor of claim 13, wherein the second capacitorplate includes a second capacitive surface that is coplanar with theplurality of mechanical bearing contacts.
 15. The force sensor of claim14, wherein the second capacitive surface and the plurality ofmechanical bearing contacts are composed of the same substrate.
 16. Theforce sensor of claim 13, wherein the planar support surface is part ofan interconnect system to transmit a signal developed in response to thechange in capacitance between the first capacitor plate and the secondcapacitor plate.
 17. The force sensor of claim 1, wherein the first andsecond capacitor plates are separated by a volume, and wherein the ratioof the height of the volume to the volume's greatest breadth is lessthan 0.05.
 18. The force sensor of claim 1, further comprising: forcesignal development means for developing a signal in response to thechange in capacitance between the first capacitor plate and the secondcapacitor plate.
 19. The force sensor of claim 1, wherein the forcesensor includes an axis of sensitivity that passes through the elasticcenter of the elastic element.
 20. The force sensor of claim 1, furthercomprising: the touch surface, wherein the touch surface is a touchsurface of a handheld device.
 21. The force sensor of claim 1, whereinthe second capacitor plate is separated by a capacitive gap from thefirst capacitor plate, the length of the mechanical path defining thecapacitive gap being no greater than one-fifth of the maximum distancebetween any two force sensors that are used in the touch location deviceto measure the touch force.
 22. A force sensor for sensing a touch forceapplied to a touch surface, the force sensor comprising: a firstsubstantially planar element comprising: a first capacitor plate havinga first capacitive surface; and an elastic element comprising anintegral elevated feature of the first capacitor plate, the elasticelement receiving at least part of the touch force into the firstelement; and a second element including a second capacitor plate opposedto the first capacitor plate; wherein transmission of at least part ofthe touch force through the elastic element contributes to a change incapacitance between the first capacitor plate and the second capacitorplate.
 23. A force sensor for sensing a touch force applied to a touchsurface, the force sensor comprising: a first element including anelastic element and a first capacitor plate including a first capacitivesurface, the elastic element and the first capacitive surface beingsubstantially coplanar; a second element including a second capacitorplate; wherein transmission of at least part of the touch force throughthe elastic element contributes to a change in capacitance between thefirst capacitor plate and the second capacitor plate.
 24. The forcesensor of claim 23, wherein the first capacitor plate and the elasticelement are integral.
 25. The force sensor of claim 23, wherein theelastic element is produced by forming an elevated feature into thefirst capacitor plate.
 26. The force sensor of claim 23, wherein thefirst and second capacitor plates are separated by a volume, the ratioof the height of the volume to the volume's greatest breadth being lessthan 0.05.
 27. A force sensor for sensing a touch force applied to atouch surface, the force sensor comprising: a first element including anelastic element, a first capacitor plate including a first capacitivesurface, force-receiving means for receiving at least part of the touchforce into the first element, force-transmitting means for transmittingat least part of the touch force to structures not including the firstelement; a second element including a second capacitor plate; andwherein transmission of at least part of the touch force through theelastic element contributes to a change in capacitance between the firstcapacitor plate and the second capacitor plate; and wherein the smallestrectangular parallelepiped that encloses the first capacitive surface,the elastic element, and the second capacitor plate has a greatestdimension that is at least five times its least dimension.
 28. The forcesensor of claim 27, wherein the elastic element comprises theforce-receiving means.
 29. The force sensor of claim 27, wherein theelastic element and the first capacitor plate are integral.
 30. Theforce sensor of claim 27, wherein the second element comprises a planarsupport surface that includes a plurality of electrically conductivemechanical bearing contacts; wherein the second capacitor plate includesa second capacitive surface that is coplanar with the plurality ofmechanical bearing contacts; and wherein at least portions of the firstcapacitor plate are in contact with the plurality of mechanical bearingcontacts to transmit force thereto.
 31. The force sensor of claim 30,wherein the planar support surface is part of an interconnect system totransmit a signal developed in response to the change in capacitancebetween the first capacitor plate and the second capacitor plate.
 32. Aforce sensor for sensing a touch force applied to a touch surface, theforce sensor comprising: a first element including a first capacitorplate including a first capacitive surface; a second element including asecond capacitor plate having a second capacitive surface, at least aportion of the first element being in contact with at least one supportregion of the second element to transmit force thereto, the secondcapacitive surface being substantially coplanar with the at least onesupport region; and wherein transmission of at least part of the touchforce to the first element contributes to a change in capacitancebetween the first capacitor plate and the second capacitor plate. 33.The force sensor of claim 32, wherein the at least one support region ispart of an interconnect system to transmit a signal developed inresponse to the change in capacitance between the first capacitor plateand the second capacitor plate.
 34. A force sensor for sensing a touchforce applied to a touch surface, the force sensor comprising: a firstelement including a first capacitor plate including a first capacitivesurface; a second element including a second capacitor plate, the secondelement being part of an interconnect system to transmit a signaldeveloped in response to the change in capacitance between the firstcapacitor plate and the second capacitor plate, at least a portion ofthe first element being in contact with at least one support region ofthe second element to transmit force thereto; wherein transmission of atleast part of the touch force to the first element contributes to achange in capacitance between the first capacitor plate and the secondcapacitor plate.
 35. The force sensor of claim 34, wherein the secondcapacitive surface and the at least one support surface are integral.36. A force sensor for sensing a touch force applied to a touch surface,the force sensor comprising: a first element including a first capacitorplate including a first capacitive surface; a second element including asecond capacitor plate separated by a capacitive gap from the firstcapacitor plate, the length of the mechanical path defining thecapacitive gap being no greater than four times the maximum dimension ofthe volume of the capacitive gap; wherein transmission of at least partof the touch force to the first element contributes to a change incapacitance between the first capacitor plate and the second capacitorplate.
 37. The force sensor of claim 36, wherein the second capacitorplate is separated from the first capacitor plate in the unloaded stateof the force sensor by not more than 10 mils.
 38. A force sensor forsensing a touch force applied to a touch surface, the force sensorcomprising: a first element including a first capacitor plate includinga first capacitive surface; a second element including a secondcapacitor plate separated by a capacitive gap from the first capacitorplate, the aggregate normal component of the mechanical path definingthe capacitive gap being no greater than twice the size of thecapacitive gap; wherein transmission of at least part of the touch forceto the first element contributes to a change in capacitance between thefirst capacitor plate and the second capacitor plate.
 39. The forcesensor of claim 38, wherein the average width of the capacitive gap inan unloaded state of the force sensor is not less than thirty times theaverage height of the capacitive gap in the unloaded state of the forcesensor.
 40. A force sensor for sensing a touch force applied to a touchsurface, the force sensor comprising: a first element includingforce-receiving means for receiving at least part of the touch forceinto the first element and a first capacitor plate including a firstcapacitive surface; a second element including a second capacitor plateseparated by a capacitive gap from the first capacitor plate, whereinthe average width of the capacitive gap in an unloaded state of theforce sensor is not less than thirty times the average height of thecapacitive gap in the unloaded state of the force sensor; whereintransmission of at least part of the touch force to the first elementcontributes to a change in capacitance between the first capacitor plateand the second capacitor plate.
 41. A force sensor for sensing a touchforce applied to a touch surface, the force sensor comprising: a firstelement including an elastic element, and a first capacitor plateincluding a first capacitive surface; and a second element including asecond capacitor plate; wherein transmission of at least part of thetouch force through the elastic element contributes to a change incapacitance between the first capacitor plate and the second capacitorplate; and wherein the force sensor has a normal stiffness not less than0.5 pounds per mil.
 42. A force sensing touch location devicecomprising: a touch surface; a bezel enclosing a first portion of thetouch surface; and force transmission means including an enclosingportion enclosing a second portion of the touch surface, said forcetransmission means having a stiffness greater than that of the bezel,wherein the force transmission means includes a path to transmit forcefrom the bezel to a region not including the touch surface.
 43. Theforce sensing touch location device of claim 42, wherein the regioncomprises a stiff surface.
 44. The force sensing touch location deviceof claim 43, wherein the touch surface is disposed between the bezel andthe stiff surface.
 45. The force sensing touch location device of claim42, wherein the portion enclosing the touch surface is narrow.
 46. Theforce sensing touch location device of claim 45, wherein the forcetransmission means comprises at least one thin rigid leg in contact withthe bezel and the region not including the touch surface.
 47. The forcesensing touch location device of claim 42, wherein a flange of the forcetransmission means encloses the second portion of the touch surface. 48.The force sensing touch location device of claim 42, wherein the forcecomprises a force that is perpendicular to the touch surface.
 49. Theforce sensing touch location device of claim 42, wherein the pathcomprises a frame surrounding the touch surface.
 50. The force sensingtouch location device of claim 49, wherein the frame comprises the forcetransmission means.
 51. The force sensing touch location device of claim43, wherein the stiff surface comprises a surface of a display device.52. The force sensing touch location device of claim 51, wherein thedisplay surface comprises an LCD device surface.
 53. The device of claim42, wherein said force transmission means provides attachment for avertically compliant seal between said bezel and said touch surface. 54.The device of claim 53, further comprising the vertically compliantseal.
 55. The device of claim 53, wherein the attachment comprises aflange of the force transmission means.
 56. The force sensing touchlocation device of claim 53, wherein the force transmission meanscomprises a rigid flange coupled to the bezel.
 57. The force sensingtouch location device of claim 54, wherein the force transmission meansprovides a bearing region to receive perpendicular forces establishingan additional seal between said force transmission means and the bezel,said bezel perpendicularly overlying at least a line of junction of saidvertically compliant seal and said force transmission means.
 58. Thedevice of claim 49, wherein said frame provides attachment for a lateralstiffening means between said frame and said touch surface.
 59. Thedevice of claim 49, wherein said frame provides an attachment forreceiving both a vertically compliant seal and a lateral stiffeningmeans.
 60. The device of claim 59, wherein the seal and the lateralstiffening means are the same element.
 61. The device of claim 59,wherein the attachment comprises a rigid bearing edge.
 62. The device ofclaim 49, wherein the frame includes an attachment for receiving boththe vertically compliant seal and a surface of the bezel that acts as asecond seal.
 63. The device of claim 42, wherein the bezel includes analignment feature for aligning the touch surface within the enclosure.64. The force sensing touch location device of claim 42, wherein thenarrow portion closely invests, but does not touch, the touch displaysurface around the periphery of the touch display.
 65. The force sensingtouch location device of claim 42, further comprising: a handheldcomputing device including the touch surface, the bezel, and the forcetransmission means.
 66. A force sensing touch location devicecomprising: a touch surface; a bezel enclosing a first portion of thetouch surface; and force transmission means including an enclosingportion enclosing a second portion of the touch surface and at least onethin rigid leg in contact with the bezel and a stiff surface notincluding the touch surface, said force transmission means having astiffness greater than that of the bezel, wherein the force transmissionmeans includes a path to transmit force from the bezel to the stiffsurface not including the touch surface.
 67. A force sensing touchlocation device comprising: a touch surface defining a touch plane; afirst rigid member; a contoured first film coupled to the touch surfaceand the first rigid member to form a first seal therebetween, thecontoured first film being compliant along an axis normal to the touchplane.
 68. The force sensing touch location device of claim 67, whereinsaid contoured first film contacts a second rigid member and whereinsaid contoured first film is disposed between the second rigid memberand the first rigid member to form a second seal between the contouredfirst film and the second rigid member.
 69. The force sensing touchlocation device of claim 68, wherein the second rigid member contactssaid contoured first film over a portion of said first rigid member. 70.The force sensing touch location device of claim 68, wherein the firstseal comprises a seal between the touch surface and a surrounding frame.71. The force sensing touch location device of claim 70, wherein thefirst rigid member comprises a portion of the frame.
 72. The forcesensing touch location device of claim 71, wherein the second sealcomprises a seal between the frame and a bezel enclosing the touchsurface, and wherein the first rigid member receives perpendicularforces from the bezel to establish the second seal, a portion of saidbezel overlying a line of junction of said first seal and said frame.73. The force sensing touch location device of claim 71, wherein thecontoured first film includes a bulge between the touch surface and theframe, and wherein the bulge is compliant along the axis normal to thetouch plane.
 74. The force sensing touch location device of claim 70,wherein the second seal comprises: a bezel including a slot; an insertremovably engaged in the slot; and a second film covering at least aportion of the force sensing touch surface.
 75. The force sensing touchlocation device of claim 67, wherein the contoured first film istransparent.
 76. The force sensing touch location device of claim 75,wherein the contoured first film comprises a transparent film having aportion overlaying at least part of the touch surface.
 77. The forcesensing touch location device of claim 76, wherein the transparent filmoverlays the entire touch surface.
 78. The force sensing touch locationdevice of claim 71, wherein a portion of the contoured first filmextends from the rigid supporting member to the touch surface, whereby agap is formed between the portion of the contoured first film and aportion of the touch surface.
 79. The force sensing touch locationdevice of claim 67, wherein a portion of the contoured first filmextends from the rigid supporting member to the touch surface in adirection not parallel to the touch plane.
 80. The force sensing touchlocation device of claim 67, wherein the contoured first film and thetouch surface comprise a monolithic element.
 81. A method for measuringthe touch force applied to the touch surface using the force sensor ofclaim 1, the method comprising a step of: (A) developing a signal basedon the change in capacitance between the first capacitor plate and thesecond capacitor plate.
 82. The method of claim 81, wherein theamplitude of the signal is a monotonic function of the change incapacitance between the first capacitor plate and the second capacitorplate.
 83. The method of claim 81, further comprising a step of: (B)measuring a property of the touch force based on the signal.
 84. Themethod of claim 83, wherein the step (B) comprises a step of measuringthe amplitude of a component of the touch force that is perpendicular tothe touch surface.
 85. The method of claim 83, wherein the step (B)comprises a step of measuring a location on the touch surface at whichthe touch force is applied.
 86. In a force sensor, a method forseparating a first capacitor plate from a second capacitor plate by adesired volume, the method comprising steps of: (A) disposing aseparator between a support surface and a principal element includingthe first capacitor plate to maintain a separation of at least thedesired volume between the first capacitor plate and the secondcapacitor plate; (B) coupling at least one region of the principalelement to at least one region of the support surface; and (C) removingthe separator, whereby the first capacitor plate and the secondcapacitor plate remain separated by at least the desired volume in anunloaded state of the force sensor.
 87. The method of claim 86, whereinthe support surface comprises the second capacitor plate.
 88. The methodof claim 86, wherein the support surface is part of an interconnectsystem to transmit a signal developed in response to the change incapacitance between the first capacitor plate and the second capacitorplate.
 89. The method of claim 86, wherein the principal element and theat least one region of the support surface are substantially parallel.90. The method of claim 86, wherein the at least one region of theprincipal element and the at least one region of the support surface areelectrically conductive, and wherein the step (B) comprises a step ofcoupling the at least one region of the principal element to at leastone region of the support surface with an electrically conductivesubstrate.
 91. The method of claim 86, wherein the separator comprises ashim.
 92. The method of claim 86, wherein the method further comprises astep of: (D) prior to the step (B), selecting a substantially planarsheet of material as the principal element.
 93. The method of claim 86,wherein the step (A) comprises disposing a predetermined substratebetween the support surface and the principal element, and wherein thestep (B) comprises a step of using the predetermined substrate to couplethe at least one region of the principal element to the at least oneregion of the support surface.
 94. In a force sensor, a method forseparating a first capacitor plate from a second capacitor plate by adesired volume, the method comprising steps of: (A) disposing apredetermined substrate containing particles of controlled size betweena support surface and a principal element including the first capacitorplate to produce a separation of at least the desired volume between thefirst capacitor plate and the second capacitor plate; and (B) couplingat least one region of the principal element to at least one region ofthe support surface to maintain the separation of at least the desiredvolume between the first capacitor plate and the second capacitor plate.95. The method of claim 94, wherein the step (A) comprises a step offlowing the predetermined substrate in a fluid state between theprincipal element and the support surface, and wherein the step (B)comprises a step of allowing the predetermined substrate to transitioninto a solid state.
 96. A method for manufacturing a force sensor, themethod comprising steps of: (A) selecting a principle element includinga substantially flat surface and a first capacitive surface; (B)disposing the first capacitive surface in opposition to a secondcapacitive surface; and (C) forming an elevated elastic feature into thesubstantially flat surface, whereby transmission of a force through theelevated elastic feature contributes to a change in capacitance betweenthe first capacitor plate and the second capacitor plate.
 97. The methodof claim 96, wherein the substantially flat surface and the firstcapacitive surface are integral.
 98. The method of claim 96, wherein thestep (A) comprises a step of selecting a sheet of electricallyconductive material as the principal element.
 99. The method of claim96, further comprising a step of: (D) placing the elevated elasticfeature in communication with a touch surface to which the force isapplied, whereby the elevated elastic feature provides a region of loadtransmission from the touch surface to the principal element.
 100. In aforce sensor, a method for separating a first capacitor plate from asecond capacitor plate by a desired volume, the method comprising stepsof: (A) disposing a separator between the second capacitor plate and asubstantially planar principal element including the first capacitorplate to maintain a separation of at least the desired volume betweenthe first capacitor plate and the second capacitor plate; (B) couplingat least one region of the principal element to at least one region ofthe support surface that is substantially parallel to the principalelement; and (C) removing the separator, whereby the first capacitorplate and the second capacitor plate remain separated by at least thedesired volume in an unloaded state of the capacitive force sensor. 101.A force sensing touch location device comprising: a touch surfacestructure to which a touch force may be applied, the touch forceincluding a perpendicular component that is perpendicular to a touchsurface of the touch surface structure and a tangential component thatis tangential to the touch surface of the touch surface structure; asupporting structure; at least one force sensor, in communication withthe touch surface and the supporting structure, to measure properties ofthe touch force; lateral restraint means, in contact with both the touchsurface structure and the supporting structure, for impeding lateralmotion of the touch surface structure without substantially impedingtransmission of the perpendicular component of the touch force throughthe at least one force sensor.
 102. The force sensing touch locationdevice of claim 101, wherein the lateral restraint means comprises athin member in contact with both the touch surface structure and thesupporting structure.
 103. The force sensing touch location device ofclaim 102, wherein the thin member joins the touch surface to asurrounding frame.
 104. The force sensing touch location device of claim103, wherein the thin member comprises at least one strip of tape. 105.The force sensing touch location device of claim 102, wherein the thinmember is constructed of high-modulus material to be substantially stiffto tangential movement of the touch surface and substantially compliantto perpendicular motion of the touch surface.
 106. The force sensingtouch location device of claim 101, wherein the touch surface comprisesa display surface.
 107. The force sensing touch location device of claim101, wherein the touch surface comprises a touch overlay overlaying adisplay surface.
 108. The force sensing touch location device of claim101, wherein the lateral restraint means comprises a preload spring.109. The force sensing touch location device of claim 108, wherein thepreload spring is fastened to an edge of the touch surface.
 110. Theforce sensing touch location device of claim 108, wherein the preloadspring has a non-uniform unloaded curvature.